When Data ONTAP performs a RAID-level scrub, it checks the disk blocks of all disks on the storage system for media errors and parity consistency. You can control the impact this operation has on system performance with the raid.verify.perf_impact option.
When RAID-level scrubbing and mirror verification are running at the same time, Data ONTAP limits the combined resource utilization to the greater 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.
If there are times during the day when the load on your storage system is decreased, you can also limit the performance impact of the automatic RAID-level scrub by changing the start time or duration of the automatic scrub.
high means that the storage system uses most of the system resources available for scrubbing; this setting can heavily affect storage system performance, but the scrub finishes sooner.
low means that the storage system uses very little of the system resources; this setting lightly affects storage system performance, but the scrub takes longer to complete.
The default impact is low.