Slow scrub performance ?

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Slow scrub performance ?

Post by jollyjinx » Tue Sep 18, 2012 2:14 pm

I'm autoscrubbing my disks every two weeks. SSD's work fine with scrub and perform well ( takes like 25 minutes two (striped) zfs ssds. But for my two mirrored 2TB harddisks it takes ages:


scan: scrub in progress since Tue Sep 18 09:01:07 2012
157Gi scanned out of 1.60Ti at 4.08Mi/s, 103h8m to go

I had that behaviour in the past with zero, but now that it's a released product I wondered if others have that problem as well ?

Patrick aka Jolly
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Re: Slow scrub performance ?

Post by alexwasserman » Tue Sep 18, 2012 2:25 pm

Last night I scrubbed a 6TB pool that consists of 1TB, 2TB, and 3TB mirrors. It's about 2.3TB utilised.

The scrub took under 6 hours.

For the first hour or so it was reporting very very slow progress - along the lines of yours. I kicked it off at midnight, around 1am it still had many days to go. At 5:30am or so it completed.

So - wait it out and see improves would be my advice.
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Re: Slow scrub performance ?

Post by jollyjinx » Tue Sep 18, 2012 2:34 pm

Yes, it will get faster over time as it has done in the past.

weird though:
a) it's already scanning 12 hours for a 75% filled 2TB mirrored pool !
b) The disks are doing nothing else but the scrub and 4Mi/s is just too slow.
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scrub guidance

Post by grahamperrin » Tue Sep 18, 2012 4:04 pm

Guidance (2012-09-14):

In some cases, the checkup (zpool scrub) operation will slow down substantially if ZFS thinks other important operations are in progress. Sometimes it can linger in this state. You have the choice of canceling the scan or for an external disk, you can unmount it and then reattach it. On remount it will resume the checkup scan.
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