Controlling the speed of disk scrubbing

About disk scrubbing

Disk scrubbing means periodically checking the disk blocks of all disks on the storage system for media errors and parity consistency.

Although disk scrubbing slows the storage system somewhat, network clients might not notice the change in storage system performance because disk scrubbing starts automatically at 1:00 a.m. on Sunday by default, when most storage systems are lightly loaded, and stops after six hours. You can change the start time with the scrub sched option, and you can change the duration time with the scrub duration option.

Changing disk scrub speed

To change the speed of disk scrubbing, complete the following step.

Step	Action
1	Enter the following command: options raid.scrub.perf_impact impact impact can be `high`, `medium`, or `low`. (default) High means that the storage system uses most of the available system resources--CPU time, disks, and FC loop bandwidth (on FC-based storage systems)--for disk scrubbing; this setting can heavily affect storage system performance. Low means that the storage system uses very little of the system resources; this setting lightly affects storage system performance.

Step

Action

Enter the following command:

options raid.scrub.perf_impact impact

impact can be high, medium, or low. (default)

High means that the storage system uses most of the available system resources--CPU time, disks, and FC loop bandwidth (on FC-based storage systems)--for disk scrubbing; this setting can heavily affect storage system performance.

Low means that the storage system uses very little of the system resources; this setting lightly affects storage system performance.

RAID operations affecting disk scrub speed

When disk scrubbing and mirror verification are running at the same time, Data ONTAP limits the combined resource utilization to the greatest impact set by either operation. For example, if raid.verify.perf_impact is set to medium and raid.scrub.perf_impact is set to low, the resource utilization by both operations has a medium impact.