8. Storage

The Storage section of the graphical interface allows you to configure the following:

  • Volumes: used to create and manage storage volumes.
  • Periodic Snapshot Tasks: used to schedule the automatic creation of filesystem snapshots.
  • Replication Tasks: used to schedule the replication of snapshots to a remote system.
  • Scrubs: used to schedule scrubs as part of ongoing disk maintenance.
  • Snapshots: used to manage local snapshots.
  • VMware-Snapshot: is used to coordinate ZFS snapshots with a VWware datastore.

These configurations are described in more detail in this section.

8.1. Volumes

The “Volumes” section of the FreeNAS® graphical interface can be used to format ZFS pools, import a disk in order to copy its data into an existing pool, or import an existing ZFS pool. It can also be used to create ZFS datasets and zvols and to manage their permissions.


in ZFS terminology, the storage that is managed by ZFS is referred to as a pool. The FreeNAS® graphical interface uses the term volume to refer to a ZFS pool.

Proper storage design is important for any NAS. It is recommended that you read through this entire chapter first, before configuring your storage disks, so that you are aware of all of the possible features, know which ones will benefit your setup most, and are aware of any caveats or hardware restrictions.

8.1.1. Volume Manager

If you have unformatted disk(s) or wish to overwrite the current filesystem and data on your disk(s), use “Volume Manager” to format the disk(s) into a ZFS pool. If you have multiple disks and are new to how ZFS handles redundancy, skim through the ZFS Primer before using “Volume Manager”.

If you click on Storage ‣ Volumes ‣ Volume Manager, you will see a screen similar to the example shown in Figure 8.1a.

Figure 8.1a: Creating a ZFS Pool Using Volume Manager


Table 8.1a summarizes the configuration options of this screen.

Table 8.1a: Options When Creating a ZFS Volume

Setting Value Description
Volume name string ZFS volumes must conform to these naming conventions; it is recommended to choose a name that will stick out in the logs (e.g. not data or freenas)
Volume to extend drop-down menu used to extend an existing ZFS pool; see Extending a ZFS Volume for instructions
Encryption checkbox read the section on Encryption before choosing to use encryption
Available disks display displays the number and size of available disks; hover over “show” to list the available device names; click the + to add all of the disks to the pool
Volume layout drag and drop click and drag the icon to select the desired number of disks for a vdev; once at least one disk is selected, the layouts supported by the selected number of disks will be added to the drop-down menu
Add Extra Device button used to configure multiple vdevs or to add log or cache devices during pool creation
Manual setup button used to make a non-optimal pool (not recommended); see Manual Setup for details

To configure the pool, drag the slider to select the desired number of disks. “Volume Manager” will display the resulting storage capacity, which takes swap into account. If you wish to change the layout or the number of disks, use the mouse to drag the slider to the desired volume layout. The “Volume layout” drop-down menu can also be clicked if a different level of redundancy is required.


for performance and capacity reasons, this screen will not allow you to create a volume from disks of differing sizes. While it is not recommended, it is possible to create a volume in this situation by using the “Manual setup” button and following the instructions in Manual Setup.

“Volume Manager” will not allow you to select a configuration if the number of disks selected is not enough to create that configuration. The following layouts are supported:

  • Stripe: requires at least one disk
  • Mirror: requires at least two disks
  • RAIDZ1: requires at least three disks
  • RAIDZ2: requires at least four disks
  • RAIDZ3: requires at least five disks
  • log device: requires at least one dedicated device, where an SSD is recommended
  • cache device: requires at least one dedicated device, where an SSD is recommended

If you have more than five disks and are using ZFS, consider the number of disks to use for best performance and scalability. An overview of the recommended disk group sizes as well as more information about log and cache devices can be found in the ZFS Primer.

The “Add Volume” button warns that existing data will be cleared. In other words, creating a new volume reformats the selected disks. If your intent is to not overwrite the data on an existing volume, click the “Cancel” button and refer to Import Disk and Import Volume to see if the existing format is supported. If so, perform that supported action instead. If the current storage format is not supported, you will need to backup the data to an external media, format the disks, then restore the data to the new volume.

Depending upon the size and number of disks, the type of controller, and whether or not encryption is selected, creating the volume may take some time. Once the volume is created, the screen will refresh and the new volume will be listed in the tree under Storage ‣ Volumes. Click the + next to the volume name to access its Change Permissions, Create Dataset, and Create zvol options. Encryption

Beginning with 8.3.1, FreeNAS® supports GELI full disk encryption when creating ZFS volumes. It is important to understand the following when considering whether or not encryption is right for your FreeNAS® system:

  • This is not the encryption method used by Oracle’s version of ZFS as that version is not open source and is the property of Oracle.
  • This is full disk encryption and not per-filesystem encryption. The underlying drives are first encrypted, then the pool is created on top of the encrypted devices.
  • This type of encryption is primarily targeted at users who store sensitive data and want to retain the ability to remove disks from the pool without having to first wipe the disk’s contents.
  • This design is only suitable for safe disposal of disks independent of the encryption key. As long as the key and the disks are intact, the system is vulnerable to being decrypted. The key should be protected by a strong passphrase and any backups of the key should be securely stored.
  • On the other hand, if the key is lost, the data on the disks is inaccessible. Always backup the key!
  • The encryption key is per ZFS volume (pool). If you create multiple pools, each pool has its own encryption key.
  • If the system has a lot of disks, there will be a performance hit if the CPU does not support AES-NI or if no crypto hardware is installed. Without hardware acceleration, there will be about a 20% performance hit for a single disk. Performance degradation will continue to increase with more disks. As data is written, it is automatically encrypted and as data is read, it is decrypted on the fly. If the processor does support the AES-NI instruction set, there should be very little, if any, degradation in performance when using encryption. This forum post compares the performance of various CPUs.
  • Data in the ARC cache and the contents of RAM are unencrypted.
  • Swap is always encrypted, even on unencrypted volumes.
  • There is no way to convert an existing, unencrypted volume. Instead, the data must be backed up, the existing pool must be destroyed, a new encrypted volume must be created, and the backup restored to the new volume.
  • Hybrid pools are not supported. In other words, newly created vdevs must match the existing encryption scheme. When extending a volume, Volume Manager will automatically encrypt the new vdev being added to the existing encrypted pool.


the encryption facility used by FreeNAS® is designed to protect against physical theft of the disks. It is not designed to protect against unauthorized software access. Ensure that only authorized users have access to the administrative GUI and that proper permissions are set on shares if sensitive data is stored on the system.

To create an encrypted volume, check the “Encryption” box shown in Figure 8.1a. A pop-up message will remind you that it is extremely important to make a backup of the key as without it the data on the disks is inaccessible. Refer to Managing Encrypted Volumes for instructions. Manual Setup

The “Manual Setup” button shown in Figure 8.1a can be used to create a non-optimal ZFS volume. While this is not recommended, it can, for example, be used to create a volume containing disks of different sizes.


when using disks of differing sizes, the volume is limited by the size of the smallest disk. For this reason, it is recommended to instead use “Volume Manager” with same-size disks.

Figure 8.1b shows the “Manual Setup” screen and Table 8.1b summarizes the available options.

Figure 8.1b: Creating a Non-Optimal ZFS Volume


Table 8.1b: Manual Setup Options

Setting Value Description
Volume name string ZFS volumes must conform to these naming conventions ; it is recommended to choose a name that will stick out in the logs (e.g. not data or freenas)
Encryption checkbox read the section on Encryption before choosing to use encryption
Member disks list highlight desired number of disks from list of available disks
Deduplication drop-down menu choices are Off, Verify, and On; carefully consider the section on Deduplication before changing this setting
ZFS Extra bullet selection used to specify if disk is used for storage (None), a log device, a cache device, or a spare Extending a ZFS Volume

The “Volume to extend” drop-down menu in Storage ‣ Volumes ‣ Volume Manager, shown in Figure 8.1a, can be used to add additional disks to an existing ZFS volume. This drop-down menu will be empty if no ZFS volume exists.


if the existing volume is encrypted, a warning message will remind you that the operation of extending a volume will reset the passphrase and recovery key. After extending the volume, you should immediately recreate both using the instructions in Managing Encrypted Volumes.

Once an existing volume has been selected from the drop-down menu, drag and drop the desired disk(s) and select the desired volume layout. For example you can:

  • select an SSD with a volume layout of “Log (ZIL)” to add a log device to the ZFS pool. Selecting 2 SSDs will create a mirrored log device.
  • select an SSD with a volume layout of “Cache (L2ARC)” to add a cache device to the ZFS pool.
  • add additional disks to increase the capacity of the ZFS pool. The caveats to doing this are described below.

When adding disks to increase the capacity of a volume, ZFS supports the addition of virtual devices, known as vdevs, to an existing ZFS pool. A vdev can be a single disk, a stripe, a mirror, a RAIDZ1, RAIDZ2, or a RAIDZ3. Once a vdev is created, you can not add more drives to that vdev; however, you can stripe a new vdev (and its disks) with the same type of existing vdev in order to increase the overall size of ZFS the pool. In other words, when you extend a ZFS volume, you are really striping similar vdevs. Here are some examples:

  • to extend a ZFS stripe, add one or more disks. Since there is no redundancy, you do not have to add the same amount of disks as the existing stripe.
  • to extend a ZFS mirror, add the same number of drives. The resulting striped mirror is a RAID 10. For example, if you have 10 drives, you could start by creating a mirror of two drives, extending this mirror by creating another mirror of two drives, and repeating three more times until all 10 drives have been added.
  • to extend a three drive RAIDZ1, add three additional drives. The result is a RAIDZ+0, similar to RAID 50 on a hardware controller.
  • to extend a RAIDZ2 requires a minimum of four additional drives. The result is a RAIDZ2+0, similar to RAID 60 on a hardware controller.

If you try to add an incorrect number of disks to the existing vdev, an error message will appear, indicating the number of disks that are needed. You will need to select the correct number of disks in order to continue.

8.1.2. Change Permissions

Setting permissions is an important aspect of configuring volumes. The graphical administrative interface is meant to set the initial permissions for a volume or dataset in order to make it available as a share. Once a share is available, the client operating system should be used to fine-tune the permissions of the files and directories that are created by the client.

The chapter on Sharing contains configuration examples for several types of permission scenarios. This section provides an overview of the screen that is used to set permissions.

Once a volume or dataset is created, it will be listed by its mount point name in Storage ‣ Volumes ‣ View Volumes. If you click the “Change Permissions” icon for a specific volume/dataset, you will see the screen shown in Figure 8.1c. Table 8.1c summarizes the options in this screen.

Figure 8.1c: Changing Permissions on a Volume or Dataset


Table 8.1c: Options When Changing Permissions

Setting Value Description
Apply Owner (user) checkbox uncheck to prevent new permission change from being applied to “Owner (user)”, see NOTE below
Owner (user) drop-down menu user to control the volume/dataset; users which were manually created or imported from a directory service will appear in the drop-down menu
Apply Owner (group) checkbox uncheck to prevent new permission change from being applied to “Owner (group)”, see NOTE below
Owner (group) drop-down menu group to control the volume/dataset; groups which were manually created or imported from a directory service will appear in the drop-down menu
Apply Mode checkbox uncheck to prevent new permission change from being applied to “Mode”, see NOTE below
Mode checkboxes only applies to the Unix or Mac “Permission Type” so will be greyed out if Windows is selected
Permission Type bullet selection choices are Unix, Mac or Windows; select the type which matches the type of client accessing the volume/dataset
Set permission recursively checkbox if checked, permissions will also apply to subdirectories of the volume/dataset; if data already exists on the volume/dataset, change the permissions on the client side to prevent a performance lag


the “Apply Owner (user)”, “Apply Owner (group)”, and “Apply Mode” checkboxes allow you to fine-tune the change permissions behavior. By default, all boxes are checked and FreeNAS® resets the owner, group, and mode whenever the “Change” button is clicked. These checkboxes allow you to fine-tune which settings to change. For example, to just change the “Owner (group)” setting, uncheck the boxes “Apply Owner (user)” and “Apply Mode”.

If you have a mix of operating systems or clients will be accessing the volume/dataset using a non-CIFS share, select the Unix “Permission Type” as all clients understand them.

The Windows “Permission Type” augments traditional Unix permissions with ACLs. Use the Windows “Permission Type” for CIFS shares or when the FreeNAS® system is a member of an Active Directory domain.

If you change your mind about the “Permission Type”, you do not have to recreate the volume/dataset as existing data is not lost. However, if you change from Windows to Unix or Mac, the extended permissions provided by ACLs will be removed from the existing files.

When you select the Windows “Permission Type”, the ACLs are set to what Windows sets on new files and directories by default. The Windows client should then be used to fine-tune the permissions as required.

8.1.3. Create Dataset

An existing ZFS volume can be divided into datasets. Permissions, compression, deduplication, and quotas can be set on a per-dataset basis, allowing more granular control over access to storage data. A dataset is similar to a folder in that you can set permissions; it is also similar to a filesystem in that you can set properties such as quotas and compression as well as create snapshots.


ZFS provides thick provisioning using quotas and thin provisioning using reserved space.

If you select an existing ZFS volume in the tree then click “Create Dataset”, you will see the screen shown in Figure 8.1d.

Figure 8.1d: Creating a ZFS Dataset


Table 8.1d summarizes the options available when creating a ZFS dataset. Some settings are only available in “Advanced Mode”. To see these settings, either click the “Advanced Mode” button or configure the system to always display these settings by checking the box “Show advanced fields by default” in System ‣ Advanced. Most attributes, except for the “Dataset Name”, “Case Sensitivity”, and “Record Size”, can be changed after dataset creation by highlighting the dataset name and clicking its “Edit Options” button in Storage ‣ Volumes ‣ View Volumes.

Table 8.1d: ZFS Dataset Options

Setting Value Description
Dataset Name string mandatory; input a unique name for the dataset
Compression Level drop-down menu see the section on Compression for a description of the available algorithms
Share type drop-down menu select the type of share that will be used on the dataset; choices are UNIX for an NFS share, Windows for a CIFS share, or Mac for an AFP share
Case Sensitivity drop-down menu choices are sensitive (default, assumes filenames are case sensitive), insensitive (assumes filenames are not case sensitive), or mixed (understands both types of filenames)
Enable atime Inherit, On, or Off controls whether the access time for files is updated when they are read; setting this property to Off avoids producing log traffic when reading files and can result in significant performance gains
Quota for this dataset integer only available in “Advanced Mode”; default of 0 disables quotas; specifying a value means to use no more than the specified size and is suitable for user datasets to prevent users from hogging available space
Quota for this dataset and all children integer only available in “Advanced Mode”; a specified value applies to both this dataset and any child datasets
Reserved space for this dataset integer only available in “Advanced Mode”; default of 0 is unlimited; specifying a value means to keep at least this much space free and is suitable for datasets containing logs which could take up all available free space
Reserved space for this dataset and all children integer only available in Advanced Mode; a specified value applies to both this dataset and any child datasets
ZFS Deduplication drop-down menu read the section on Deduplication before making a change to this setting
Record Size drop-down menu only available in “Advanced Mode”; while ZFS automatically adapts the record size dynamically to adapt to data, if the data has a fixed size (e.g. a database), matching that size may result in better performance

Once a dataset is created, you can click on that dataset and select “Create Dataset”, thus creating a nested dataset, or a dataset within a dataset. You can also create a zvol within a dataset. When creating datasets, double-check that you are using the “Create Dataset” option for the intended volume or dataset. If you get confused when creating a dataset on a volume, click all existing datasets to close them–the remaining “Create Dataset” will be for the volume. Deduplication

Deduplication is the process of not creating duplicate copies of data in order to save space. Depending upon the amount of duplicate data, deduplicaton can improve storage capacity as less data is written and stored. However, the process of deduplication is RAM intensive and a general rule of thumb is 5 GB RAM per TB of storage to be deduplicated. In most cases, using compression instead of deduplication will provide a comparable storage gain with less impact on performance.

In FreeNAS®, deduplication can be enabled during dataset creation. Be forewarned that there is no way to undedup the data within a dataset once deduplication is enabled as disabling deduplication has NO EFFECT on existing data. The more data you write to a deduplicated dataset, the more RAM it requires and when the system starts storing the DDTs (dedup tables) on disk because they no longer fit into RAM, performance craters. Furthermore, importing an unclean pool can require between 3-5 GB of RAM per TB of deduped data, and if the system doesn’t have the needed RAM it will panic, with the only solution being to add more RAM or to recreate the pool. Think carefully before enabling dedup! This article provides a good description of the value versus cost considerations for deduplication.

Unless you have a lot of RAM and a lot of duplicate data, do not change the default deduplication setting of “Off”. For performance reasons, consider using compression rather than turning this option on.

If deduplication is changed to On, duplicate data blocks are removed synchronously. The result is that only unique data is stored and common components are shared among files. If deduplication is changed to Verify, ZFS will do a byte-to-byte comparison when two blocks have the same signature to make sure that the block contents are identical. Since hash collisions are extremely rare, Verify is usually not worth the performance hit.


once deduplication is enabled, the only way to disable it is to use the zfs set dedup=off dataset_name command from Shell. However, any data that is already stored as deduplicated will not be un-deduplicated as only newly stored data after the property change will not be deduplicated. The only way to remove existing deduplicated data is to copy all of the data off of the dataset, set the property to off, then copy the data back in again. Alternately, create a new dataset with “ZFS Deduplication” left as disabled, copy the data to the new dataset, and destroy the original dataset. Compression

When selecting a compression type, you need to balance performance with the amount of disk space saved by compression. Compression is transparent to the client and applications as ZFS automatically compresses data as it is written to a compressed dataset or zvol and automatically decompresses that data as it is read. The following compression algorithms are supported:

  • lz4: recommended compression method as it allows compressed datasets to operate at near real-time speed. This algorithm only compresses the files that will benefit from compression. By default, ZFS pools made using FreeNAS® 9.2.1 or higher use this compression method, meaning that this algorithm is used if the “Compression level” is left at Inherit when creating a dataset or zvol.
  • gzip: varies from levels 1 to 9 where gzip fastest (level 1) gives the least compression and gzip maximum (level 9) provides the best compression but is discouraged due to its performance impact.
  • zle: fast but simple algorithm to eliminate runs of zeroes.
  • lzjb: provides decent data compression, but is considered deprecated as lz4 provides much better performance.

If you select Off as the “Compression level” when creating a dataset or zvol, compression will not be used on the dataset/zvol. This is not recommended as using lz4 has a negligible performance impact and allows for more storage capacity.

8.1.4. Create zvol

A zvol is a feature of ZFS that creates a raw block device over ZFS. This allows you to use a zvol as an iSCSI device extent.

To create a zvol, select an existing ZFS volume or dataset from the tree then click “Create zvol” to open the screen shown in Figure 8.1e.

Figure 8.1e: Creating a zvol


The configuration options are described in Table 8.1e. Some settings are only available in “Advanced Mode”. To see these settings, either click the “Advanced Mode” button or configure the system to always display these settings by checking the box “Show advanced fields by default” in System ‣ Advanced.

Table 8.1e: zvol Configuration Options

Setting Value Description
zvol Name string mandatory; input a name for the zvol
Size for this zvol integer specify size and value such as 10Gib; if the size is more than 80% of the available capacity, the creation will fail with an “out of space” error unless the “Force size” box is checked
Force size checkbox by default, the system will not let you create a zvol if that operation will bring the pool to over 80% capacity; while NOT recommended, checking this box will force the creation of the zvol in this situation
Compression level drop-down menu see the section on Compression for a description of the available algorithms
Sparse volume checkbox used to provide thin provisioning; use with caution for when this option is selected, writes will fail when the pool is low on space
Block size drop-down menu only available in “Advanced Mode” and by default is based on the number of disks in pool; can be set to match the block size of the filesystem which will be formatted onto the iSCSI target

8.1.5. Import Disk

The Volume ‣ Import Disk screen, shown in Figure 8.1f, is used to import a single disk that has been formatted with the UFS, NTFS, MSDOS, or EXT2/3 filesystem. The import is meant to be a temporary measure in order to copy the data from a disk to an existing ZFS dataset. Only one disk can be imported at a time.

Figure 8.1f: Importing a Disk


Use the drop-down menu to select the disk to import, select the type of filesystem on the disk, and browse to the ZFS dataset that will hold the copied data. When you click “Import Volume”, the disk will be automatically mounted, its contents will be copied to the specified ZFS dataset, and the disk will automatically unmount once the copy operation completes.

8.1.6. Import Volume

If you click Storage ‣ Volumes ‣ Import Volume, you can configure FreeNAS® to use an existing ZFS pool. This action is typically performed when an existing FreeNAS® system is re-installed. Since the operating system is separate from the storage disks, a new installation does not affect the data on the disks. However, the new operating system needs to be configured to use the existing volume.

Figure 8.1g shows the initial pop-up window that appears when you select to import a volume.

Figure 8.1g: Initial Import Volume Screen


If you are importing an unencrypted ZFS pool, select “No: Skip to import” to open the screen shown in Figure 8.1h.

Figure 8.1h: Importing a Non-Encrypted Volume


Existing volumes should be available for selection from the drop-down menu. In the example shown in Figure 8.1h, the FreeNAS® system has an existing, unencrypted ZFS pool. Once the volume is selected, click the “OK” button to import the volume.

If an existing ZFS pool does not show in the drop-down menu, run zpool import from Shell to import the pool.

If you plan to physically install ZFS formatted disks from another system, be sure to export the drives on that system to prevent an “in use by another machine” error during the import.

If you suspect that your hardware is not being detected, run camcontrol devlist from Shell. If the disk does not appear in the output, check to see if the controller driver is supported or if it needs to be loaded using Tunables. Importing an Encrypted Pool

If you are importing an existing GELI-encrypted ZFS pool, you must decrypt the disks before importing the pool. In Figure 8.1g, select “Yes: Decrypt disks” to access the screen shown in Figure 8.1i.

Figure 8.1i: Decrypting the Disks Before Importing the ZFS Pool


Select the disks in the encrypted pool, browse to the location of the saved encryption key, input the passphrase associated with the key, then click “OK” to decrypt the disks.


the encryption key is required to decrypt the pool. If the pool can not be decrypted, it can not be re-imported after a failed upgrade or lost configuration. This means that it is very important to save a copy of the key and to remember the passphrase that was configured for the key. Refer to Managing Encrypted Volumes for instructions on how to manage the keys for encrypted volumes.

Once the pool is decrypted, it should appear in the drop-down menu of Figure 8.1h. Click the “OK” button to finish the volume import.

8.1.7. View Disks

Storage ‣ Volumes ‣ View Disks allows you to view all of the disks recognized by the FreeNAS® system. An example is shown in Figure 8.1j.

Figure 8.1j: Viewing Disks


The current configuration of each device is displayed. Click a disk’s entry and then its “Edit” button to change its configuration. The configurable options are described in Table 8.1f.

Table 8.1f: Disk Options

Setting Value Description
Name string read-only value showing FreeBSD device name for disk
Serial string read-only value showing the disk’s serial number
Description string optional
HDD Standby drop-down menu indicates the time of inactivity (in minutes) before the drive enters standby mode in order to conserve energy; this forum post demonstrates how to determine if a drive has spun down
Advanced Power Management drop-down menu default is Disabled, can select a power management profile from the menu
Acoustic Level drop-down menu default is Disabled; can be modified for disks that understand AAM
Enable S.M.A.R.T. checkbox enabled by default if the disk supports S.M.A.R.T.; unchecking this box will disable any configured S.M.A.R.T. Tests for the disk
S.M.A.R.T. extra options string additional smartctl(8) options

Clicking a disk’s entry will also display its “Wipe” button which can be used to blank a disk while providing a progress bar of the wipe’s status. Use this option before discarding a disk.


should a disk’s serial number not be displayed in this screen, use the smartctl command within Shell. For example, to determine the serial number of disk ada0, type smartctl -a /dev/ada0 | grep Serial.

8.1.8. View Volumes

If you click Storage ‣ Volumes ‣ View Volumes, you can view and further configure existing ZFS pools, datasets, and zvols. The example shown in Figure 8.1k demonstrates one ZFS pool (volume1) with two datasets (the one automatically created with the pool, volume1, and dataset1) and one zvol (zvol1).

Note that in this example, there are two datasets named volume1. The first represents the ZFS pool and its “Used” and “Available” entries reflect the total size of the pool, including disk parity. The second represents the implicit or root dataset and its “Used” and “Available” entries indicate the amount of disk space available for storage.

Buttons are provided for quick access to “Volume Manager”, “Import Disk”, “Import Volume”, and “View Disks”. If the system has multipath-capable hardware, an extra button will be added to “View Multipaths”. The columns indicate the “Name” of the volume/dataset/zvol, how much disk space is “Used”, how much disk space is “Available”, the type of “Compression”, the “Compression Ratio”, and the “Status” of the pool.

Figure 8.1k: Viewing Volumes


If you click the entry for a pool, several buttons will appear at the bottom of the screen. In order from left to right, these buttons are used to perform the following:

Detach Volume: allows you to either export the pool or to delete the contents of the pool, depending upon the choice you make in the screen shown in Figure 8.1l. The “Detach Volume” screen displays the current used space and indicates if there are any shares, provides checkboxes to “Mark the disks as new (destroy data)” and to “Also delete the share’s configuration”, asks if you are sure that you want to do this, and the browser will turn red to alert you that you are about to do something that will make the data inaccessible. If you do not check the box to mark the disks as new, the volume will be exported. This means that the data is not destroyed and the volume can be re-imported at a later time. If you will be moving a ZFS pool from one system to another, perform this export action first as it flushes any unwritten data to disk, writes data to the disk indicating that the export was done, and removes all knowledge of the pool from the system. If you do check the box to mark the disks as new, the pool and all the data in its datasets, zvols, and shares will be destroyed and the underlying disks will be returned to their raw state.

Figure 8.1l: Detaching or Deleting a Volume


Scrub Volume: scrubs and how to schedule them are described in more detail in Scrubs. This button allows you to manually initiate a scrub. Since a scrub is I/O intensive and can negatively impact performance, you should not initiate one while the system is busy. A “Cancel” button is provided should you need to cancel a scrub. If you do cancel a scrub, the next scrub will start over from the beginning, not where the cancelled scrub left off. To view the current status of a running scrub or the statistics from the last completed scrub, click the “Volume Status” button.

Volume Status: as seen in the example in Figure 8.1m, this screen shows the device name and status of each disk in the ZFS pool as well as any read, write, or checksum errors. It also indicates the status of the latest ZFS scrub. If you click the entry for a device, buttons will appear to edit the device’s options (shown in Figure 8.1n), offline or online the device, or replace the device (as described in Replacing a Failed Drive).

Upgrade: used to upgrade the pool to the latest ZFS features, as described in Upgrading a ZFS Pool. This button will not appear if the pool is running the latest versions of feature flags.

Figure 8.1m: Volume Status


If you click a disk in “Volume Status” and click its “Edit Disk” button, you will see the screen shown in Figure 8.1n. Table 8.1f summarizes the configurable options.

Figure 8.1n: Editing a Disk



versions of FreeNAS® prior to 8.3.1 required a reboot in order to apply changes to the “HDD Standby”, “Advanced Power Management”, and “Acoustic Level” settings. As of 8.3.1, changes to these settings are applied immediately.

If you click a dataset in Storage ‣ Volumes ‣ View Volumes, six buttons will appear at the bottom of the screen. In order from left to right, these buttons allow you to:

Change Permissions: allows you to edit the dataset’s permissions as described in Change Permissions.

Create Snapshot: allows you to create a one-time snapshot. If you wish to schedule the regular creation of snapshots, instead use Periodic Snapshot Tasks.

Destroy Dataset: if you click the “Destroy Dataset” button, the browser will turn red to indicate that this is a destructive action. The “Destroy Dataset” screen forces you to check the box “I’m aware this will destroy all child datasets and snapshots within this dataset” before it will perform this action.

Edit Options: allows you to edit the volume’s properties described in Table 8.1d. Note that it will not let you change the dataset’s name.

Create Dataset: used to create a child dataset within this dataset.

Create zvol: allows you to create a child zvol within this dataset.

If you click a zvol in Storage ‣ Volumes ‣ View Volumes, three icons will appear at the bottom of the screen: “Create Snapshot”, “Edit zvol”, and “Destroy zvol”. Similar to datasets, you can not edit a zvol’s name and you will need to confirm that you wish to destroy the zvol. Managing Encrypted Volumes

If you check the “Encryption” box during the creation of a pool, five additional buttons will be added to the entry for the pool in Storage ‣ Volumes ‣ View Volumes. An example is seen in Figure 8.1o.

Figure 8.1o: Encryption Icons Associated with an Encrypted Pool


In order from left to right, these additional encryption buttons are used to:

Create/Change Passphrase: click this button to set and confirm the passphrase associated with the GELI encryption key. You will be prompted to input and repeat the desired passphrase and a red warning reminds you to “Remember to add a new recovery key as this action invalidates the previous recovery key”. Unlike a password, a passphrase can contain spaces and is typically a series of words. A good passphrase is easy to remember (like the line to a song or piece of literature) but hard to guess (people who know you should not be able to guess the passphrase). Remember this passphrase as you can not re-import an encrypted volume without it. In other words, if you forget the passphrase, the data on the volume can become inaccessible if you need to re-import the pool. Protect this passphrase as anyone who knows it could re-import your encrypted volume, thwarting the reason for encrypting the disks in the first place.

Once the passphrase is set, the name of this button will change to “Change Passphrase”. After setting or changing the passphrase, it is important to immediately create a new recovery key by clicking the “Add recovery key” button. This way, if the passphrase is forgotten, the associated recovery key can be used instead.

Download Key: click this icon to download a backup copy of the GELI encryption key. The encryption key is saved to the client system, not on the FreeNAS® system. You will be prompted to input the password used to access the FreeNAS® administrative GUI before the selecting the directory in which to store the key. Since the GELI encryption key is separate from the FreeNAS® configuration database, it is highly recommended to make a backup of the key. If the key is every lost or destroyed and there is no backup key, the data on the disks is inaccessible.

Encryption Re-key: generates a new GELI encryption key. Typically this is only performed when the administrator suspects that the current key may be compromised. This action also removes the current passphrase.

Add recovery key: generates a new recovery key. This screen will prompt you to input the password used to access the FreeNAS® administrative GUI and then to select the directory in which to save the key. Note that the recovery key is saved to the client system, not on the FreeNAS® system. This recovery key can be used if the passphrase is forgotten. Always immediately add a recovery key whenever the passphrase is changed.

Remove recover key: Typically this is only performed when the administrator suspects that the current recovery key may be compromised. Immediately create a new passphrase and recovery key.


the passphrase, recovery key, and encryption key need to be protected. Do not reveal the passphrase to others. On the system containing the downloaded keys, take care that that system and its backups are protected. Anyone who has the keys has the ability to re-import the disks should they be discarded or stolen.

8.1.9. View Multipaths

FreeNAS® uses gmultipath(8) to provide multipath I/O support on systems containing hardware that is capable of multipath. An example would be a dual SAS expander backplane in the chassis or an external JBOD.

Multipath hardware adds fault tolerance to a NAS as the data is still available even if one disk I/O path has a failure.

FreeNAS® automatically detects active/active and active/passive multipath-capable hardware. Any multipath-capable devices that are detected will be placed in multipath units with the parent devices hidden. The configuration will be displayed in Storage ‣ Volumes ‣ View Multipaths. Note that this option will not be displayed in the Storage ‣ Volumes tree on systems that do not contain multipath-capable hardware.

8.1.10. Replacing a Failed Drive

If you are using any form of redundant RAID, you should replace a failed drive as soon as possible to repair the degraded state of the RAID. Depending upon the capability of your hardware, you may or may not need to reboot in order to replace the failed drive. AHCI capable hardware does not require a reboot.


striping (RAID0) does not provide redundancy. If you lose a disk in a stripe, the volume will be destroyed and you will need to recreate the volume and restore the data from backup.


if your pool is encrypted with GELI, refer to Replacing an Encrypted Drive before proceeding.

Before physically removing the failed device, go to Storage ‣ Volumes ‣ View Volumes. Next, select your volume’s name. At the bottom of the interface you will see several icons, one of which is “Volume Status”. Click the “Volume Status” icon and locate the failed disk. Once you have located the failed device in the GUI, perform the following steps:

  1. If the disk is formatted with ZFS, click the disk’s entry then its “Offline” button in order to change that disk’s status to OFFLINE. This step is needed to properly remove the device from the ZFS pool and to prevent swap issues. If your hardware supports hot-pluggable disks, click the disk’s “Offline” button, pull the disk, then skip to step 3. If there is no “Offline” button but only a “Replace” button, then the disk is already offlined and you can safely skip this step.


    if the process of changing the disk’s status to OFFLINE fails with a “disk offline failed - no valid replicas” message, you will need to scrub the ZFS volume first using its “Scrub Volume” button in Storage ‣ Volumes ‣ View Volumes. Once the scrub completes, try to “Offline” the disk again before proceeding.

  2. If the hardware is not AHCI capable, shutdown the system in order to physically replace the disk. When finished, return to the GUI and locate the OFFLINE disk.

  3. Once the disk has been replaced and is showing as OFFLINE, click the disk again and then click its “Replace” button. Select the replacement disk from the drop-down menu and click the “Replace Disk” button. If the disk is a member of an encrypted ZFS pool, the menu will also prompt you to input and confirm the passphrase for the pool. Once you click the “Replace Disk” button, the ZFS pool will start to resilver and the status of the resilver will be displayed.

In the example shown in Figure 8.1p, a failed disk is being replaced by disk ada5 in the volume named volume1.

Figure 8.1p: Replacing a Failed Disk


Once the resilver is complete, “Volume Status” will show a “Completed” resilver status and indicate if there were any errors. Figure 8.1q indicates that the disk replacement was successful for this example.

Figure 8.1q: Disk Replacement is Complete

_images/replace2.png Replacing an Encrypted Drive

If the ZFS pool is encrypted, additional steps are needed when replacing a failed drive.

First, make sure that a passphrase has been set using the instructions in Encryption before attempting to replace the failed drive. Then, follow the steps 1 and 2 as described above. During step 3, you will be prompted to input and confirm the passphrase for the pool. Enter this information then click the “Replace Disk” button. Wait until the resilvering is complete.

Next, restore the encryption keys to the pool. If the following additional steps are not performed before the next reboot, you may lose access to the pool permanently.

  1. Highlight the pool that contains the disk you just replaced and click the “Encryption Re-key” button in the GUI. You will need to enter the root password.
  2. Highlight the pool that contains the disk you just replaced and click the “Create Passphrase” button and enter the new passphrase. You can reuse the old passphrase if desired.
  3. Highlight the pool that contains the disk you just replaced and click the “Download Key” button in order to save the new encryption key. Since the old key will no longer function, any old keys can be safely discarded.
  4. Highlight the pool that contains the disk you just replaced and click the “Add Recovery Key” button in order to save the new recovery key. The old recovery key will no longer function, so it can be safely discarded. Removing a Log or Cache Device

If you have added any log or cache devices, these devices will also appear in Storage ‣ Volumes ‣ View Volumes ‣ Volume Status. If you click the device, you can either use its “Replace” button to replace the device as described above, or click its “Remove” button to remove the device.

Before performing either of these operations, verify the version of ZFS running on the system by running zpool upgrade -v|more from Shell.

If the pool is running ZFSv15, and a non-mirrored log device fails, is replaced, or removed, the pool is unrecoverable and the pool must be recreated and the data restored from a backup. For other ZFS versions, removing or replacing the log device will lose any data in the device which had not yet been written. This is typically the last few seconds of writes.

Removing or replacing a cache device will not result in any data loss, but may have an impact on read performance until the device is replaced.

8.1.11. Replacing Drives to Grow a ZFS Pool

The recommended method for expanding the size of a ZFS pool is to pre-plan the number of disks in a vdev and to stripe additional vdevs using Volume Manager as additional capacity is needed.

However, this is not an option if you do not have open drive ports or the ability to add a SAS/SATA HBA card. In this case, you can replace one disk at a time with a larger disk, wait for the resilvering process to incorporate the new disk into the pool completes, then repeat with another disk until all of the disks have been replaced.

The safest way to perform this is to use a spare drive port or an eSATA port and a hard drive dock. In this case, you can perform the following steps:

  1. Shut down the system.
  2. Install one new disk.
  3. Start up the system.
  4. Go to Storage ‣ Volumes, select the pool to expand and click the “Volume Status” button. Select a disk and click the “Replace” button. Choose the new disk as the replacement.
  5. You can view the status of the resilver process by running zpool status. When the new disk has resilvered, the old one will be automatically offlined. You can then shut down the system and physically remove the replaced disk. One advantage of this approach is that there is no loss of redundancy during the resilver.

If you do not have a spare drive port, you will need to replace one drive with a larger drive using the instructions in Replacing a Failed Drive. This process is slow and places the system in a degraded state. Since a failure at this point could be disastrous, do not attempt this method unless the system has a reliable backup. Replace one drive at a time and wait for the resilver process to complete on the replaced drive before replacing the next drive. Once all the drives are replaced and the resilver completes, you should see the added space in the pool.


either method requires the ZFS property “autoexpand”. Check and verify that the autoexpand property is enabled before attempting to grow the pool. If it is not, the pool will not recognize that the disk capacity has increased. By default, this property is enabled in FreeNAS® versions 8.3.1 and higher.

To verify the autoexpand property, run this command from Shell, replacing Vol1 with the name of the volume to expand:

zpool get autoexpand Vol1
NAME   PROPERTY        VALUE                   SOURCE
Vol1   autoexpand      on                      local

If autoexpansion is not enabled, enable it by specifying the name of the ZFS volume:

zpool set autoexpand=on Vol1

8.1.12. Enabling ZFS Pool Expansion

It is recommended to enable the autoexpand property before you start replacing drives. If the property is not enabled before replacing some or all of the drives, extra configuration is needed to inform ZFS of the expanded capacity.

Verify that autoexpand is set as described in the previous section. Then, bring each of the drives back online with the following command, replacing the volume name and GPT ID for each disk in the ZFS pool:

zpool online -e Vol1 gptid/xxx

Online one drive at a time and check the status using the following example. If a drive starts to resilver, you need to wait for the resilver to complete before proceeding to online the next drive.

To find the GPT ID information for the drives, use zpool status Pool_Name which will also show you if any drives are failed or in the process of being resilvered:

zpool status Vol1
pool: Vol1
state: ONLINE
scan: scrub repaired 0 in 16h24m with 0 errors on Sun Mar 10 17:24:20 2013
NAME                                           STATE   READ WRITE CKSUM
Vol1                                           ONLINE  0    0     0
raidz1-0                                       ONLINE  0    0     0
gptid/d5ed48a4-634a-11e2-963c-00e081740bfe     ONLINE  0    0     0
gptid/03121538-62d9-11e2-99bd-00e081740bfe     ONLINE  0    0     0
gptid/252754e1-6266-11e2-8088-00e081740bfe     ONLINE  0    0     0
gptid/9092045a-601d-11e2-892e-00e081740bfe     ONLINE  0    0     0
gptid/670e35bc-5f9a-11e2-92ca-00e081740bfe     ONLINE  0    0     0

errors: No known data errors

After onlining all of the disks, type zpool status to see if the drives start to resilver. If this happens, wait for the resilvering process to complete.

Next, export and then import the pool:

zpool export Vol1

zpool import -R /mnt Vol1

Once the import completes, all of the drive space should be available. Verify that the increased size is recognized:

zpool list Vol1
Vol1   9.06T   1.41T   7.24T   31%     1.00x   ONLINE  /mnt

If you cannot see the extra space, you may need to run zpool online -e pool_name device_name for every device listed in zpool status.

8.1.13. Splitting a Mirrored Pool

ZFSv28 provides the ability to to split a mirrored storage pool, which detaches a disk or disks in the original ZFS volume in order to create another identical ZFS volume on another system.


this operation only works on mirrored ZFS volumes.

In this example, a ZFS mirror named test contains three drives:

zpool status
 pool: test
state: ONLINE
scan: resilvered 568K in 0h0m with 0 errors on Wed Jul 6 16:10:58 2011
test           ONLINE  0    0     0
mirror-0       ONLINE  0    0     0
da1            ONLINE  0    0     0
da0            ONLINE  0    0     0
da4            ONLINE  0    0     0

The following command splits from the existing three disk mirror test a new ZFS volume named migrant containing one disk, da4. Disks da0 and da1 remain in test:

zpool split test migrant da4

At this point, da4 can be physically removed and installed to a new system as the new pool is exported as it is created. Once physically installed, import the identical pool on the new system:

zpool import migrant

This makes the ZFS volume migrant available with a single disk. Be aware that properties come along with the clone, so the new pool will be mounted where the old pool was mounted if the mountpoint property was set on the original pool.

Verify the status of the new pool:

zpool status
 pool: migrant
state: ONLINE
scan: resilvered 568K in 0h0m with 0 errors on Wed Jul 6 16:10:58 2011
migrant        ONLINE  0    0     0
da4            ONLINE  0    0     0

errors: No known data errors

On the original system, the status now looks like this:

zpool status
 pool: test
state: ONLINE
scan: resilvered 568K in 0h0m with 0 errors on Wed Jul 6 16:10:58 2011

test           ONLINE  0    0     0
mirror-0       ONLINE  0    0     0
da1            ONLINE  0    0     0
da0            ONLINE  0    0     0

errors: No known data errors

At this point, it is recommended to add disks to create a full mirror set. This example adds two disks named da2 and da3:

zpool attach migrant da4 da2

zpool attach migrant da4 da3

The migrant volume now looks like this:

zpool status
 pool: migrant
state: ONLINE
scan: resilvered 572K in 0h0m with 0 errors on Wed Jul 6 16:43:27 2011
migrant        ONLINE  0    0     0
mirror-0       ONLINE  0    0     0
da4            ONLINE  0    0     0
da2            ONLINE  0    0     0
da3            ONLINE  0    0     0

Now that the new system has been cloned, you can detach da4 and install it back to the original system. Before physically removing the disk, run this command on the new system:

zpool detach migrant da4

Once the disk is physically re-installed, run this command on the original system:

zpool attach orig da0 da4

Should you ever need to create a new clone, remember to remove the old clone first:

zpool destroy migrant

8.2. Periodic Snapshot Tasks

A periodic snapshot task allows you to schedule the creation of read-only versions of ZFS volumes and datasets at a given point in time. Snapshots can be created quickly and, if little data changes, new snapshots take up very little space. For example, a snapshot where no files have changed takes 0 MB of storage, but as you make changes to files, the snapshot size changes to reflect the size of the changes.

Snapshots provide a clever way of keeping a history of files, should you need to recover an older copy or even a deleted file. For this reason, many administrators take snapshots often (e.g. every 15 minutes), store them for a period of time (e.g. for a month), and store them on another system (e.g. using Replication Tasks). Such a strategy allows the administrator to roll the system back to a specific time or, if there is a catastrophic loss, an off-site snapshot can restore the system up to the last snapshot interval.

Before you can create a snapshot, you need to have an existing ZFS volume. How to create a volume is described in Volume Manager.

To create a periodic snapshot task, click Storage ‣ Periodic Snapshot Tasks ‣ Add Periodic Snapshot which will open the screen shown in Figure 8.2a. Table 8.2a summarizes the fields in this screen.


if you just need a one-time snapshot, instead use Storage ‣ Volumes ‣ View Volumes and click the “Create Snapshot” button for the volume or dataset that you wish to snapshot.

Figure 8.2a: Creating a Periodic Snapshot


Table 8.2a: Options When Creating a Periodic Snapshot

Setting Value Description
Volume/Dataset drop-down menu select an existing ZFS volume, dataset, or zvol
Recursive checkbox select this box to take separate snapshots of the volume/dataset and each of its child datasets; if unchecked, only one snapshot is taken of the specified Volume/Dataset
Lifetime integer and drop-down menu how long to keep the snapshot on this system; if the snapshot is replicated, it is not removed from the receiving system when the lifetime expires
Begin drop-down menu do not create snapshots before this time of day
End drop-down menu do not create snapshots after this time of day
Interval drop-down menu how often to take snapshot between Begin and End times
Weekday checkboxes which days of the week to take snapshots
Enabled checkbox uncheck to disable the scheduled replication task without deleting it

If the “Recursive” box is checked, you do not need to create snapshots for every dataset individually as they are included in the snapshot. The downside is that there is no way to exclude certain datasets from being included in a recursive snapshot.

Once you click the “OK” button, a snapshot will be taken and this task will be repeated according to your settings.

After creating a periodic snapshot task, an entry for the snapshot task will be added to “View Periodic Snapshot Tasks”. Click an entry to access its “Edit” and “Delete” buttons.

8.3. Replication Tasks

A replication task allows you to automate the copy of ZFS snapshots to another system over an encrypted connection. This allows you to create an off-site backup of a ZFS dataset or pool.

This section will refer to the system generating the ZFS snapshots as PUSH and the system to receive a copy of the ZFS snapshots as PULL.

Before you can configure a replication task, the following pre-requisites must be met:

  • a ZFS pool must exist on both PUSH and PULL.
  • a periodic snapshot task must be created on PUSH. You will not be able to create a replication task before the first snapshot exists.
  • the SSH service must be enabled on PULL. The first time the service is enabled, it will generate the required SSH keys.

A replication task uses the following keys:

  • /data/ssh/replication.pub: the RSA public key used for authenticating the PUSH replication user. This key needs to be copied to the replication user account on PULL.
  • /etc/ssh/ssh_host_rsa_key.pub: the RSA host public key of PULL used to authenticate the receiving side in order to prevent a man-in-the-middle attack. This key needs to be copied to the replication task on PUSH.

This section will demonstrate how to configure a replication task between the following two FreeNAS® systems:

  • will be referred to as PUSH. This system has a periodic snapshot task for the ZFS dataset /mnt/local/data.
  • will be referred to as PULL. This system has an existing ZFS volume named /mnt/remote which will store the pushed snapshots.

8.3.1. Configure PULL

A copy of the public key for the replication user on PUSH needs to be pasted to the public key of the replication user on the PULL system.

To obtain a copy of the replication key: on PUSH go to Storage ‣ Replication Tasks ‣ View Replication Tasks. Click the “View Public Key” button and copy its contents. An example is shown in Figure 8.3a.

Figure 8.3a: Copy the Replication Key


Go to PULL and click Account ‣ Users ‣ View Users. Click the “Modify User” button for the user account you will be using for replication (by default this is the root user). Paste the copied key into the “SSH Public Key” field and click “OK”. If a key already exists, append the new text after the existing key.

On PULL, ensure that the SSH service is enabled in Services ‣ Control Services. Start it if it is not already running.

8.3.2. Configure PUSH

On PUSH, verify that a periodic snapshot task has been created and that at least one snapshot is listed in Storage ‣ Snapshots.

To create the replication task, click Storage ‣ Replication Tasks ‣ Add Replication which will open the screen shown in Figure 8.3b. For this example, the required configuration is as follows:

  • the Volume/Dataset is local/data
  • the Remote ZFS Volume/Dataset is remote
  • the Remote hostname is
  • the Begin and End times are at their default values, meaning that replication will occur whenever a snapshot is created
  • once the Remote hostname is input, click the “SSH Key Scan” button; assuming the address is reachable and the SSH service is running on PULL, its key will automatically be populated to the “Remote hostkey” box

Figure 8.3b: Adding a Replication Task


Table 8.3a summarizes the available options in the “Add Replication” screen.

Table 8.3a: Adding a Replication Task

Setting Value Description
Volume/Dataset drop-down menu the ZFS volume or dataset on PUSH containing the snapshots to be replicated; the drop-down menu will be empty if a snapshot does not already exist
Remote ZFS Volume/Dataset string the ZFS volume on PULL that will store the snapshots; /mnt/ is assumed and should not be included in the path
Recursively replicate checkbox if checked will also replicate child datasets
Delete stale snapshots checkbox if checked, will delete any previous snapshots on PULL which are no longer stored on PUSH
Replication Stream Compression drop-down menu choices are lz4 (fastest), pigz (all rounder), plzip (best compression), or Off (no compression); selecting a compression algorithm can reduce the size of the data being replicated
Limit (kB/s) integer limits replication speed to specified value in kilobytes/second; default of 0 is unlimited
Begin drop-down menu the replication can not start before this time; the times selected in the “Begin” and “End” fields set the replication window for when replication can occur
End drop-down menu the replication must start by this time; once started, replication will occur until it is finished (see NOTE below)
Enabled checkbox uncheck to disable the scheduled replication task without deleting it
Remote hostname string IP address or DNS name of PULL
Remote port string must match port being used by SSH service on PULL
Dedicated User Enabled checkbox allows a user account other than root to be used for replication
Dedicated User drop-down menu only available if “Dedicated User Enabled” is checked; select the user account to be used for replication
Encryption Cipher drop-down menu choices are Standard, Fast, or Disabled; temporarily selecting Disabled can significantly reduce the time for the initial replication
Remote hostkey string use the “SSH Key Scan” button to retrieve the public key of PULL

By default, replication occurs when snapshots occur. For example, if snapshots are scheduled for every 2 hours, replication occurs every 2 hours. The initial replication can take a significant period of time, from many hours to possibly days, as the structure of the entire ZFS pool needs to be recreated on the remote system. The actual time will depend upon the size of the pool and the speed of the network. Subsequent replications will take far less time, as only the modified data will be replicated. If the security policy allows it, temporarily change the “Encryption Cipher” to Disabled until the initial replication is complete. This will turn off encryption but will speed up the replication. The “Encryption Cipher” can then be changed to Standard or Fast for subsequent replications.

The “Begin” and “End” times can be used to create a window of time where replication occurs. The default times allow replication to occur at any time of the day a snapshot occurs. Change these times if snapshot tasks are scheduled during office hours but the replication itself should occur after office hours. For the “End” time, consider how long replication will take so that it finishes before the next day’s office hours begin.

Once the replication task is saved, PUSH will immediately attempt to replicate its latest snapshot to PULL. If the replication is successful, the snapshot will appear in the Storage ‣ Snapshots tab of PULL. Also, the “Last snapshot sent to remote side” and “Status” fields of Storage ‣ Snapshots on PUSH will indicate when the last snapshot was successfully sent to that “Remote Hostname”. If the snapshot is not replicated, refer to Troubleshooting Replication for troubleshooting tips.

8.3.3. Troubleshooting Replication

If you have followed all of the steps above and have PUSH snapshots that are not replicating to PULL, check to see if SSH is working properly. On PUSH, open Shell and try to ssh into PULL. Replace hostname_or_ip with the value for PULL:

ssh -vv -i /data/ssh/replication hostname_or_ip

This command should not ask for a password. If it asks for a password, SSH authentication is not working. Go to Storage ‣ Replication Tasks and click the “View Public Key” button. Make sure that it matches one of the values in /~/.ssh/authorized_keys on PULL, where ~ represents the home directory of the replication user.

Also check /var/log/auth.log on PULL and /var/log/messages on PUSH to see if either log gives an indication of the error.

If the key is correct and replication is still not working, try deleting all snapshots on PULL except for the most recent one. In Storage ‣ Snapshots check the box next to every snapshot except for the last one (the one with 3 icons instead of 2), then click the global “Destroy” button at the bottom of the screen.

Once you have only one snapshot, open Shell on PUSH and use the zfs send command. To continue our example, the ZFS snapshot on the local/data dataset of PUSH is named auto-20110922.1753-2h, the IP address of PULL is, and the ZFS volume on PULL is remote. Note that the @ is used to separate the volume/dataset name from the snapshot name:

zfs send local/data@auto-20110922.1753-2h | ssh -i /data/ssh/replication zfs receive local/data@auto-20110922.1753-2h


if the zfs send fails, open Shell on PULL and use the zfs destroy -R volume_name@snapshot_name command to delete the stuck snapshot. You can then use the zfs list -t snapshot on PULL to confirm if the snapshot successfully replicated.

After successfully transmitting the snapshot, recheck again after the time period between snapshots lapses to see if the next snapshot successfully transmitted. If it is still not working, you can manually send the specified snapshot with this command:

zfs send local/data@auto-20110922.1753-2h | ssh -i /data/ssh/replication zfs receive local/data@auto-20110922.1753-2h

8.4. Scrubs

Storage ‣ Scrubs allows you to schedule and manage scrubs on a ZFS volume. Performing a ZFS scrub on a regular basis helps to identify data integrity problems, detects silent data corruptions caused by transient hardware issues, and provides early alerts to disk failures. If you have consumer-quality drives, consider a weekly scrubbing schedule. If you have datacenter-quality drives, consider a monthly scrubbing schedule.

Depending upon the amount of data, a scrub can take a long time. Scrubs are I/O intensive and can negatively impact performance. They should be scheduled for evenings or weekends to minimize the impact to users.

A ZFS scrub only checks used disk space. To check unused disk space, schedule S.M.A.R.T. Tests of “Type” of Long Self-Test to run once or twice a month.

When you create a volume that is formatted with ZFS, a ZFS scrub is automatically scheduled for you. An entry of the same volume name is added to Storage ‣ Scrubs and a summary of this entry can be viewed in Storage ‣ Scrubs ‣ View Scrubs. Figure 8.4a displays the default settings for the volume named volume1. In this example, the entry has been highlighted and the “Edit” button clicked in order to display the “Edit” screen. Table 8.4a summarizes the options in this screen.

Figure 8.4a: Viewing a Volume’s Default Scrub Settings


Table 8.4a: ZFS Scrub Options

Setting Value Description
Volume drop-down menu select ZFS volume to scrub
Threshold days integer number of days since the last scrub completed before the next scrub can occur, regardless of the calendar schedule; the default is a multiple of 7 which should ensure that the scrub always occurs on the same day of the week
Description string optional
Minute slider or minute selections if use the slider, scrub occurs every N minutes; if use minute selections, scrub starts at the highlighted minutes
Hour slider or hour selections if use the slider, scrub occurs every N hours; if use hour selections, scrub occurs at the highlighted hours
Day of Month slider or month selections if use the slider, scrub occurs every N days; if use month selections, scrub occurs on the highlighted days of the selected months
Month checkboxes scrub occurs on the selected months
Day of week checkboxes scrub occurs on the selected days; default is Sunday to least impact users
Enabled checkbox uncheck to disable the scheduled scrub without deleting it

You should review the default selections and, if necessary, modify them to meet the needs of your environment.

While a “Delete” button is provided, deleting a scrub is not recommended as a scrub provides an early indication of disk issues that could lead to a disk failure. If you find that a scrub is too intensive for your hardware, consider unchecking the “Enabled” button for the scrub as a temporary measure until the hardware can be upgraded.

8.5. Snapshots

The “Snapshots” tab can be used to review the listing of available snapshots. An example is shown in Figure 8.5a.


if snapshots do not appear, check that the current time configured in Periodic Snapshot Tasks does not conflict with the “Begin”, “End”, and “Interval” settings. If the snapshot was attempted but failed, an entry will be added to /var/log/messages. This log file can be viewed in Shell.

Figure 8.5a: Viewing Available Snapshots


The listing will include the name of the volume or dataset, the name of each snapshot, and the amount of used and referenced data, where:

Used: indicates the amount of space consumed by this dataset and all its descendents. This value is checked against this dataset’s quota and reservation. The space used does not include this dataset’s reservation, but does take into account the reservations of any descendent datasets. The amount of space that a dataset consumes from its parent, as well as the amount of space that are freed if this dataset is recursively destroyed, is the greater of its space used and its reservation. When a snapshot is created, its space is initially shared between the snapshot and the filesystem, and possibly with previous snapshots. As the filesystem changes, space that was previously shared becomes unique to the snapshot, and is counted in the snapshot’s space used. Additionally, deleting snapshots can increase the amount of space unique to (and used by) other snapshots. The amount of space used, available, or referenced does not take into account pending changes. While pending changes are generally accounted for within a few seconds, disk changes do not necessarily guarantee that the space usage information is updated immediately.

Refer: indicates the amount of data that is accessible by this dataset, which may or may not be shared with other datasets in the pool. When a snapshot or clone is created, it initially references the same amount of space as the file system or snapshot it was created from, since its contents are identical.

It will also indicate if the snapshot has been replicated to a remote system.

The most recent snapshot will have 3 icons. The icons associated with a snapshot allow you to:

Clone Snapshot: will prompt for the name of the clone to create. The clone will be a writable copy of the snapshot. Since a clone is really a dataset which can be mounted, the clone will appear in the “Active Volumes” tab, instead of the “Periodic Snapshots” tab, and will have the word clone in its name.

Destroy Snapshot: a pop-up message will ask you to confirm this action. Child clones must be destroyed before their parent snapshot can be destroyed. While creating a snapshot is instantaneous, deleting a snapshot can be I/O intensive and can take a long time, especially when deduplication is enabled. In order to delete a block in a snapshot, ZFS has to walk all the allocated blocks to see if that block is used anywhere else; if it is not, it can be freed.

Rollback Snapshot: a pop-up message will ask if you are sure that you want to rollback to this snapshot state. If you click “Yes”, any files that have changed since the snapshot was taken will be reverted back to their state at the time of the snapshot.


rollback is a potentially dangerous operation and will cause any configured replication tasks to fail as the replication system uses the existing snapshot when doing an incremental backup. If you do need to restore the data within a snapshot, the recommended steps are:

  1. Clone the desired snapshot.
  2. Share the clone with the share type or service running on the FreeNAS® system.
  3. Once users have recovered the needed data, destroy the clone in the Active Volumes tab.

This approach will never destroy any on-disk data and has no impact on replication.

Periodic snapshots can be configured to appear as shadow copies in newer versions of Windows Explorer, as described in Configuring Shadow Copies. Users can access the files in the shadow copy using Explorer without requiring any interaction with the FreeNAS® graphical administrative interface.

The ZFS Snapshots screen allows you to create filters to view snapshots by selected criteria. To create a filter, click the “Define filter” icon (near the text “No filter applied”). When creating a filter:

  • select the column or leave the default of “Any Column”.
  • select the condition. Possible conditions are: contains (default), is, starts with, ends with, does not contain, is not, does not start with, does not end with, and is empty.
  • input a value that meets your view criteria.
  • click the “Filter” button to save your filter and exit the define filter screen. Alternately, click the “+” button to add another filter.

If you create multiple filters, select the filter you wish to use before leaving the define filter screen. Once a filter is selected, the “No filter applied” text will change to “Clear filter”. If you click “Clear filter”, a pop-up message will indicate that this will remove the filter and all available snapshots will be listed.

8.6. VMware-Snapshot

Storage ‣ VMware-Snapshot allows you to coordinate ZFS snapshots when using VMware as a datastore. Once this type of snapshot is created, FreeNAS® will automatically snapshot any running VMware virtual machines before taking a scheduled or manual ZFS snapshot of the dataset or zvol backing that VMware datastore. The temporary VMware snapshots are then deleted on the VMware side but still exist in the ZFS snapshot and can be used as stable resurrection points in that snapshot. These coordinated snapshots will be listed in Snapshots.

Figure 8.6a shows the menu for adding a VMware snapshot and Table 8.6a summarizes the available options.

Figure 8.6a: Adding a VMware Snapshot


Table 8.6a: VMware Snapshot Options

Setting Value Description
Hostname string IP address or hostname of VMware host; when clustering, this is the vCenter server for the cluster
Username string user on VMware host with enough permission to snapshot virtual machines
Password string password associated with “Username”
ZFS Filesystem drop-down menu the filesystem to snapshot
Datastore drop-down menu after inputting the “Hostname”, “Username”, and “Password”, click the “Fetch Datastores” button to populate the menu and select the datastore to synchronize with