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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 11:27:29 -0600
Cc: "developers@xxxxxxxxxxxxxxxxxx" <developers@xxxxxxxxxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <54F88CEC.4030009@xxxxxxxxxxxxxxxxxx>
References: <54EC958E.2000001@xxxxxxxxxxxxxxxxxx> <20150224215907.GA18360@dastard> <54EF1A8F.7030505@xxxxxxxxxxxxxxxxxx> <54F856E7.10006@xxxxxxxxxxxxxxxxxx> <54F87BF3.3000405@xxxxxxxxxxx> <54F88CEC.4030009@xxxxxxxxxxxxxxxxxx>
On 3/5/15 11:05 AM, Harry wrote:
> Thanks for the reply Eric.
> 
> One of our problems is that we're limited in terms of what
> manipulations we can apply to the live system, and so instead we've
> been running our experiments against the backup system, and you're
> quite right that DRBD may be introducing some weirdness of its own,
> so those experiments may not be safe to draw conclusions from.
> 
> Here's what we know about the live system
> -> it had an outage, equivalent to having its power cable yanked, or doing an 
> 'echo b > /proc/sysrq-trigger'
> -> when it came back, it decided to mount the drive without quotas.
> -> we saw a message in syslog saying " Failed to initialize disk quotas"
> -> last time we had to run a quotacheck (several months ago) it took about 2 
> hours.
> 
> We can repro the quotacheck issue on our test clusters, as follows:
> -> kick off a job that writes to the disk
> -> hard reboot with "echo b > /proc/sysrq-trigger"
> -> on next boot, see "Failed to initialize disk quotas" message, xfs mounts 
> without quotas
> -> soft reboot with "reboot"
> -> on next boot, see "Quotacheck needed: Please wait." message.
> -> Quotacheck completes some time later.
> 
> So our best-case scenario is that, next time we reboot, we'll have an
> outage of about 2 hours. And our paranoid worst-case scenario,
> induced by our experiments with our drbd backup drives, are that the
> disk will actually turn out not to be mountable at all.
> 
> is that "quotacheck always required after hard reboot" behaviour that
> we're observing something you expected? you seemed to be saying that
> the fact that quota are journaled should mean it's not needed?

In general, that's correct.  It's not clear why "Failed to initialize disk 
quotas"
appeared; that seems closer to the root cause.  But again, we don't have your
full logs to look at, I don't know if anything else offers a clue.  (For that
matter, we don't even know what kernel version you're on...)

here, on a recent 4.0-rc1 kernel:

# mount -o quota /dev/sdc6 /mnt/test
# cp -aR /lib/modules/ /mnt/test
# echo b > /proc/sysrq-trigger

[152807.209688] sysrq: SysRq : Resetting
...
<reboots>

# mount -o quota /dev/sdc6 /mnt/test
# dmesg | tail -n 3
[   90.822601] XFS (sdc6): Mounting V4 Filesystem
[   90.921346] XFS (sdc6): Starting recovery (logdev: internal)
[   93.399133] XFS (sdc6): Ending recovery (logdev: internal)
#

-Eric

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