Automatic pool rollback

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Automatic pool rollback

Post by grahamperrin » Tue Apr 02, 2013 3:02 pm

> … for drives that don’t flush correctly

Are there other situations in which rollback is, or should be, automated with ZEVO Community Edition 1.1.1?

For example, I wonder whether a rollback could or should have prevented the corruption that's observed in a recent topic.
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Re: Automatic pool rollback

Post by raattgift » Tue Apr 02, 2013 9:23 pm

Automatic pool rollback is for when the labels disagree, and is a standard cross-platform zfs feature, although there may be additional heuristics and mechanisms in the ZEVO port. It is a gentler form of zpool -F.

There is some discussion here : http://www.c0t0d0s0.org/archives/6071-N ... -fsck.html

Don't confuse pool rollback with dataset rollback (zfs rollback snapshotname).

The problem in the discussion you link to is that there is a fully consistent filesystem that nevertheless contains a bad object; rolling back a few TXGs at import time *MAY* have decommitted the bad ZAP DMU object, but it also likely would have decommitted other (possibly good and important) data at the same time. If the label txg values agree, it is almost never a good idea to roll back to previous txgs at import, especially not without involving an operator.
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Thanks

Post by grahamperrin » Wed Apr 03, 2013 1:21 am

OK – https://www.diigo.com/user/grahamperrin ... rt=created

As I think visually, I often try to picture what's on disk. There's Max Bruning's weblog: RAIDZ On-Disk Format (2009-04-09) and the well-known linked PDF, the ZFS On-Disk Specification (archived). I read parts of that PDF but intentionally, I haven't allowed it to sink it because of the draft status (dyslexia hits me in this way: if I learn something wrong, I find it very difficult to un-learn).

Now back to that other topic …
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