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What are the important changes to RAID scrub in Data ONTAP 8.3.x?

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Applies to

Clustered Data ONTAP 8.3

Answer

General higher system utilization is observed by customers after an upgrade to Data ONTAP 8.3, especially during night hours. A possible reason can be the change to the RAID scrub schedule introduced in Data ONTAP 8.3.
For more information, see of the Clustered Data ONTAP ® 8.3 Release Notes

The default RAID scrub schedule changed in Data ONTAP 8.3 - scrubs are run every day.
For more information, see page 53 of the Release Notes

If no specific value is defined, the default schedule will apply.
 
raid.scrub.schedule
 
This option specifies the weekly schedule (day, time and duration) for scrubs that started automatically. The default schedule is daily at 1 a.m. for a duration of 4 hours, except on Sunday when it is 12 hours. If an empty string ("") is specified as an argument, it will delete the previous scrub schedule and add the default schedule. One or more schedules can be specified using this option. The syntax is duration[h|m]@weekday@start_time,[duration[h|m]@weekday@start_time,...], where duration is the time period for which the scrub operation is allowed to run, in hours or minutes ('h' or 'm' respectively). If the duration is not specified, the raid.scrub.duration option value will be used as the duration for the schedule.
 
Weekday is the day on which the scrub is scheduled to start. The valid values are sun, mon, tue, wed, thu, fri, sat. start_time is the time when a scrub is scheduled to start. It is specified in a 24-hour format. Only the hour (0-23) needs to be specified. For example, options raid.scrub.schedule 240m@tue@2,8h@sat@22 will cause the scrub to start every Tuesday at 2 a.m. for 240 minutes, and every Saturday at 10 p.m. for 480 minutes.
 
Example:
Use the show command to check the current settings:

cluster::> storage raid-options show -name raid.scrub.schedule
Node     Option                                Value        Constraint
-------- ------------------------------------- ------------ -----------
cluster-01 raid.scrub.schedule                           none
cluster-02 raid.scrub.schedule                           none
2 entries were displayed.


Use the modify command to change the schedule as required:
cluster::> storage raid-options modify -node cluster-01 -name raid.scrub.schedule 240m@tue@2
Specified scrub schedule added

With the show command, you can verify the change to the schedule:
cluster::> storage raid-options show -name raid.scrub.schedule
Node     Option                                Value        Constraint
-------- ------------------------------------- ------------ -----------
cluster-01 raid.scrub.schedule              240m@tue@2   none
cluster-02 raid.scrub.schedule                           none
2 entries were displayed.


To change back to the default schedule, use the modify command again:
cluster::> storage raid-options modify -node cluster-01 -name raid.scrub.schedule ""
 
If you replace an existing schedule with an empty string "", the default scrub schedule will be added automatically.

Verification through the Event log:
You can also verify and search for the related messages using the event log show command:

Cluster-01::> event log show -messagename raid.rg.scrub.resume

[?] Tue May 24 01:00:12 CEST [cluster: config_thread: raid.rg.scrub.resume:notice]: /aggr_ssc_dc1_ds11_b_sata_root/plex0/rg0: resuming scrub at stripe 578657472 (89%% complete)
  
In this example, starting at 1AM as per the default schedule.

To check for the pausing of scrub, search for a suspend message:
Cluster-01::> event log show -messagename raid.rg.scrub.suspend

[?] Tue May 24 05:00:01 CEST [cluster: config_thread: raid.scrub.suspended:notice]: Disk scrub suspended. 


In this example, it suspends at 5AM after 4 hours runtime, as per the default schedule.

To check for the summary, run:
Cluster-01::> event log show -messagename raid.rg.scrub.summary
 
[?] Tue May 24 05:00:01 CEST [cluster: config_thread: raid.rg.scrub.summary.lw:notice]: Scrub found 0 RAID write signature inconsistencies in /aggr_ssc_dc1_ds11_b_sata_data_01/plex0/rg0.


By default, scrub will run 4 hours every day, thus the overall scrub runtime will be higher and scans will complete more frequently compared to previous versions of Data ONTAP. 
It is expected behavior that the system will have higher disk activity during this time, compared to previous releases.
 
If this is an issue during the week, the schedule can be defined to run at specific times and for specific durations.

Additional Information

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