Continuous media scrub

About continuous media scrubbing

By default, Data ONTAP runs continuous background media scrubbing for media errors on storage system disks. The purpose of the continuous media scrub is to detect and scrub media errors in order to minimize the chance of storage system disruption due to media error while a storage system is in degraded or reconstruction mode.

Negligible performance impact

Because continuous media scrubbing searches only for media errors, the impact on system performance is negligible.

Note
Media scrubbing is a continuous background process. Therefore, you might observe disk LEDs blinking on an apparently idle storage system. You might also observe some CPU activity even when no user workload is present. The media scrub attempts to exploit idle disk bandwidth and free CPU cycles to make faster progress. However, any client workload results in aggressive throttling of the media scrub resource.

Not a substitute for a scheduled disk scrub

Because the continuous process described in this section scrubs only media errors, you should continue to run the storage system's scheduled complete disk scrub operation, which is described in Automatic and manual disk scrubs. The complete disk scrub carries out parity and checksum checking and repair operations, in addition to media checking and repair operations, on a scheduled rather than a continuous basis.

Adjusting maximum time for a media scrub cycle

You can decrease the CPU resources consumed by a continuous media scrub under a heavy client workload by increasing the maximum time allowed for a media scrub cycle to complete.

By default, one cycle of a storage system's continuous media scrub can take a maximum of 72 hours to complete. In most situations, one cycle completes in a much shorter time; however, under heavy client workload conditions, the default 72-hour maximum ensures that whatever the client load is on the storage system, enough CPU resources will be allotted to the media scrub to complete one cycle in no more than 72 hours.

If you want the media scrub operation to consume even fewer CPU resources under heavy storage system client workload, you can increase the maximum number of hours for the media scrub cycle. This uses fewer CPU resources for the media scrub in times of heavy storage system usage.

To change the maximum time for a media scrub cycle, complete the following step.

Step	Action
1	Enter the following command: options raid.media_scrub.rate max_hrs_per_cycle max_hrs_per_cycle is the maximum number of hours that you want to allow for one cycle of the continuous media scrub. Valid options range from 72 to 336 hours.

Disabling continuous media scrubbing

You should keep continuous media error scrubbing enabled, particularly for R100 and R200 series storage systems, but you might decide to disable your continuous media scrub if your storage system is carrying out operations with heavy performance impact and if you have alternative measures (such as aggregate SyncMirror replication or RAID-DP configuration) in place that prevent data loss due to storage system disruption or double-disk failure.

To disable continuous media scrubbing, complete the following step.

Step	Action
1	Enter the following command at the Data ONTAP command line: options raid.media_scrub.enable off Note If you disable continuous media scrubbing, you can restart it by entering the following command: `options raid.media_scrub.enable on`

Checking media scrub activity

You can confirm media scrub activity on your storage system by completing the following step.

Step	Action
1	Entering one of the following commands: *aggr media_scrub status [/aggr[/plex][/raidgroup]] [-v]* *aggr media_scrub status [-s spare_disk_name] [-v]* /aggr[/plex] [/raidgroup] is the optional pathname to the aggregate, plex, or RAID group on which you want to confirm media scrubbing activity. `-s` disk_name specifies the optional name of a specific spare disk on which you want to confirm media scrubbing activity. `-v` is specifies the verbose version of the media scrubbing activity status. The verbose status information includes the percentage of the current scrub that is complete, the start time of the current scrub, and the completion time of the last scrub. Note If you enter `aggr media_scrub` status without specifying a pathname or a disk name, the status of the current media scrubs on all RAID groups and spare disks is displayed.

Step

Action

Entering one of the following commands:

aggr media_scrub status [/aggr[/plex][/raidgroup]] [-v]

aggr media_scrub status [-s spare_disk_name] [-v]

/aggr[/plex] [/raidgroup] is the optional pathname to the aggregate, plex, or RAID group on which you want to confirm media scrubbing activity.

-s disk_name specifies the optional name of a specific spare disk on which you want to confirm media scrubbing activity.

-v is specifies the verbose version of the media scrubbing activity status. The verbose status information includes the percentage of the current scrub that is complete, the start time of the current scrub, and the completion time of the last scrub.

Note
If you enter aggr media_scrub status without specifying a pathname or a disk name, the status of the current media scrubs on all RAID groups and spare disks is displayed.

Example 1. Checking of storage system-wide media scrubbing

The following command displays media scrub status information for all the aggregates and spare disks on the storage system.

aggr media_scrub status

aggr media_scrub /aggr0/plex0/rg0 is 0% complete

aggr media_scrub /aggr2/plex0/rg0 is 2% complete

aggr media_scrub /aggr2/plex0/rg1 is 2% complete

aggr media_scrub /aggr3/plex0/rg0 is 30% complete

aggr media_scrub 9a.8 is 31% complete

aggr media_scrub 9a.9 is 31% complete

aggr media_scrub 9a.13 is 31% complete

aggr media_scrub 9a.2 is 31% complete

aggr media_scrub 9a.12 is 31% complete

Example 2. Verbose checking of storage system-wide media scrubbing

The following command displays verbose media scrub status information for all the aggregates on the storage system.

aggr media_scrub status -v

aggr media_scrub: status of /aggr0/plex0/rg0 :

  Current instance of media_scrub is 0% complete.

  Media scrub started at Thu Mar  4 21:26:00 GMT 2004

  Last full media_scrub completed: Thu Mar  4 21:20:12 GMT 2004

aggr media_scrub: status of 9a.8 :

  Current instance of media_scrub is 31% complete.

  Media scrub started at Thu Feb 26 23:14:00 GMT 2004

  Last full media_scrub completed: Wed Mar  3 23:22:33 GMT 2004

aggr media_scrub: status of 9a.9 :

  Current instance of media_scrub is 31% complete.

  Media scrub started at Thu Feb 26 23:14:00 GMT 2004

  Last full media_scrub completed: Wed Mar  3 23:22:33 GMT 2004

aggr media_scrub: status of 9a.13 :

  Current instance of media_scrub is 31% complete.

  Media scrub started at Thu Feb 26 23:14:00 GMT 2004

  Last full media_scrub completed: Wed Mar  3 23:22:37 GM

Example 3. Checking for media scrubbing on a specific aggregate

The following command displays media scrub status information for the aggregate aggr2.

aggr media_scrub status /aggr2

  aggr media_scrub /aggr2/plex0/rg0 is 4% complete

  aggr media_scrub /aggr2/plex0/rg1 is 10% complete

Example 4. Checking for media scrubbing on a specific spare disk

The following commands display media scrub status information for the spare disk 9b.12.

aggr media_scrub status -s 9b.12

aggr media_scrub 9b.12 is 31% complete

aggr media_scrub status -s 9b.12 -v

aggr media_scrub: status of 9b.12 :

  Current instance of media_scrub is 31% complete.

  Media scrub started at Thu Feb 26 23:14:00 GMT 2004

  Last full media_scrub completed: Wed Mar  3 23:23:33 GMT 2004

Enabling continuous media scrubbing on disks

Data disks

Set the following system-wide default option to On to enable a continuous media scrub on its data disks that have been assigned to an aggregate:

options raid.media_scrub.enable

Spare disks

Set the following system-wide default option to On to enable a continuous media scrub on its spare disks:

options raid.media_scrub.enable

options raid.media_scrub.spares.enable