ZFS Scrubs
Storage → ZFS 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, detect silent data corruptions caused by transient hardware issues, and to provide 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.
NOTE: 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.
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 → ZFS Scrubs and a summary of this entry can be viewed in Storage → ZFS Scrubs → View ZFS Scrubs. Figure 6.4a displays the default Edit settings for the volume named volume1. Table 6.4a summarizes the options in this screen.
Figure 6.4a: Viewing a Volume's Default Scrub Settings
Table 6.4a: ZFS Scrub Options
| Setting | Value | Description |
| Volume | drop-down menu | select ZFS volume to scrub |
| Threshold days | integer | number of days between scrubs; the default is a multiple of 7 to ensure 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 disabling the scrub as a temporary measure until the hardware can be upgraded.
If you do delete a scrub, you can create a new scrub task by clicking Storage → Volumes → ZFS Scrubs → Add ZFS Scrub.
