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Re: trying to avoid a lengthy quotacheck by deleting all quota data

To: Harry <harry@xxxxxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Subject: Re: trying to avoid a lengthy quotacheck by deleting all quota data
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Thu, 05 Mar 2015 09:53:23 -0600
Cc: "developers@xxxxxxxxxxxxxxxxxx" <developers@xxxxxxxxxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <54F856E7.10006@xxxxxxxxxxxxxxxxxx>
References: <54EC958E.2000001@xxxxxxxxxxxxxxxxxx> <20150224215907.GA18360@dastard> <54EF1A8F.7030505@xxxxxxxxxxxxxxxxxx> <54F856E7.10006@xxxxxxxxxxxxxxxxxx>
On 3/5/15 7:15 AM, Harry wrote:
> Update -- so far, we've not managed to gain any confidence that we'll
> ever be able to re-mount that disk. The general consensus seems to be
> to fish all the data off the disk using rsync, and then move off XFS
> to ext4.
> 
> Not a very helpful message for y'all to hear, I know. But if it's any
> help in prioritising your future work, i think the dealbreaker for us
> was the inescapable quotacheck on mount, which means that any time a
> fileserver goes down unexpectedly, we have an unavoidable,
> indeterminate-but-long period of downtime...
> 
> hp

What you decide to use is up to you of course, and causes us no
heartbreak.  :)  But I think you fundamentally misunderstand the situation;
an unexpected fileserver failure should not result in a lengthy quotacheck
on xfs, because xfs quota is journaled, and will simply be replayed along with
the rest of the log.

I honestly don't know what has led you to the conclusion that remounting
the filesystem will lead to any quotacheck at all, let alone a lengthy one.

> * We're even a bit worried the disk might be in a broken state, such
> that the quotacheck won't actually complete successfully at all.

If your disk is broken, that's not a filesystem issue.  It seems possible
that whatever drbd manipulation you're doing is causing an issue, but because
you haven't really explained it in detail, I don't know.

> We take DRBD offline, so it's no longer writing, then we take
> snapshots of the drives, then remount those elsewhere so we can
> experiment without disturbing the live system.

Did you quiesce the filesystem first with i.e. xfs_freeze?

So far this thread has been long on prose and speculation, and short
on actual analysis, log messages, etc.  Feel free to use ext4 or whatever
suits you, but given that nothing in this thread has implicated misbehavior
by xfs, I don't think that switching filesystems will solve the perceived
problem.

-Eric

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