Re: Is there a best practice for adjust RAID "scrub" options?

This is normal. I forget the options at this point (dont really use them
any more) but there is a default limit as to how long scrubs will run. They
remember where they left off and pick up one week later. It also, if I
recall correctly will only do so many scrubs at the same time. Remember, it
is not just scrubbing the aggregate, but looking at each Raid Group for
consistency.

--tmac




On Thu, May 30, 2019 at 1:19 PM Sylvain Robitaille <[email protected]>
wrote:

>
> Hello NetApp Gurus.  I'm hoping mostly to get some guidance on RAID
> group scrubbing options and with some luck, perhaps pointers to
> documentation that would help me determine appropriate values in
> our environment.
>
> We've been seeing what feels like a large number of scrubbing
> "timeouts" on our filers.  Log entries similar to this one:
>
>     May 28 05:00:02 fc1-ev-n1.console.private [kern.notice]
> [fc1-ev-n1:raid.scrub.suspended.timer:notice]: Disk scrub suspended because
> the scrub time limit 240 was exceeded. It will resume at the next
> weekly/scheduled scrub.
>
> What we'd like to know is how concerned we should be about this.
> Ideally we'd be seeing "scrubs" complete reasonably frequently, but I'm
> honestly not sure how I could determine how frequently that happens,
> or how frequently it *should* happen for that matter.
>
> The scrub options on the filer have not been changed from the Ontap
> defaults (NetApp Release 9.5P2, but we've been seeing this with
> earlier versions as well):
>
>     Node    Option                  Value  Constraint
>     ------- ----------------------- ------ ----------
>     fc1-n1  raid.media_scrub.rate   600    only_one
>     fc1-n1  raid.scrub.perf_impact  low    only_one
>     fc1-n1  raid.scrub.schedule            none
>
> (and the same for the partner node, of course)
>
> The "storage raid-options" manual page indicates that the default
> schedule of daily at 1am for 4 hours, except Sundays when it runs
> for 12 hours, applies if no explicit schedule is defined.
>
> If I examine the scrub status of our aggregates:
>
>     fc1-ev::> storage aggregate scrub -aggregate * -action status
>
>     Raid Group:/e1n2_tssd/plex0/rg0, Is Suspended:false, Last Scrub:Thu
> May 30 02:39:10 2019
>     Raid Group:/e1n2_t01/plex0/rg0, Is Suspended:true, Last Scrub:Sun May
> 26 02:55:15 2019, Percentage Completed:65%
>     Raid Group:/e1n2_t02/plex0/rg0, Is Suspended:false, Last Scrub:Thu May
> 30 02:28:37 2019
>     Raid Group:/e1n2_root/plex0/rg0, Is Suspended:false, Last Scrub:Thu
> May 30 03:39:03 2019
>     Raid Group:/e1n1_root/plex0/rg0, Is Suspended:false, Last Scrub:Wed
> May 29 02:03:43 2019
>     Raid Group:/e1n1_d01/plex0/rg0, Is Suspended:true, Last Scrub:Tue May
> 28 03:22:52 2019, Percentage Completed:7%
>     Raid Group:/e1n1_d01/plex0/rg1, Is Suspended:true, Last Scrub:Wed May
> 29 02:00:56 2019, Percentage Completed:4%
>     Raid Group:/e1n1_d01/plex0/rg2, Is Suspended:false, Last Scrub:Wed May
> 29 04:02:50 2019
>     Raid Group:/e1n1_d01/plex0/rg3, Is Suspended:false, Last Scrub:Wed May
> 29 04:08:45 2019
>     Raid Group:/e1n1_d00/plex0/rg0, Is Suspended:true, Last Scrub:Sun Apr
> 28 06:00:40 2019, Percentage Completed:81%
>     Raid Group:/e1n1_d00/plex0/rg1, Is Suspended:true, Last Scrub:Sun Apr
> 28 07:38:30 2019, Percentage Completed:80%
>
> The truth is I'm not sure how to interpret this output:
>
>    - Is it the case that each RAID group where "Is Suspended:false"
>      *completed* its scrub at the "Last Scrub" time, while those that
>      are suspended are those for which we're seeing log entries?
>
>    - Given the default schedule that has the scrub run for 12 hours
>      on Sunday mornings, does it seem odd that /e1n2_t01/plex0/rg0 was
>      suspended last Sunday at 02:55:15, prior to completion?  In fact,
>      all those interrupted on a Sunday were interrupted well before
>      12 hours.  Might there be other reasons for suspending scrub
>      operations?  The load on this filer is not excessive in any way:
>      CPU utilization is typically comfortably below 50%
>
>    - How do I determine why the two RAID groups containing e1n1_d00
>      haven't run scrubbing in over a month?  Is there something I
>      should do about that?
>
> I've found documentation that explains the options and how to change
> them, but none that explains how to decide whether I *should* change
> them, or how to determine what to change them to.  I'm interpretting
> that raid.media_scrub.rate and raid.scrub.schedule could be used
> together to tune the scrubbing, but am quite unsure how to determine
> what the best values would be for our filers.  Any pointers to
> documentation that would help here would be hugely appreciated.
>
> Thanks in advance ...
>
> --
> ----------------------------------------------------------------------
> Sylvain Robitaille                               [email protected]
>
> Systems analyst / AITS                            Concordia University
> Faculty of Engineering and Computer Science   Montreal, Quebec, Canada
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