[linux-lvm] Unexptected filesytem unmount with thin provision and autoextend disabled - lvmetad crashed?

Gionatan Danti assistenza at assyoma.it
Wed May 18 13:47:23 UTC 2016

On 17/05/2016 15:48, Zdenek Kabelac wrote:
> Yes - in general - you've witnessed  general tool failure,
> and dmeventd is not 'smart' to recognize the reason of failure.
> Normally this 'error' should not happen.
> And while I'd even say there could have been a 'shortcut'
> without even reading VG 'metadata' - since there is profile support,
> it can't be known (100% threshold) without actually reading metadata
> (so it's quite tricky case anyway)

One question: I did some test (on another machine), deliberately 
killing/stopping the lvmetad service/socket. When the pool was almost 
full, the following entry was logged in /var/log/messages

WARNING: Failed to connect to lvmetad. Falling back to internal scanning.

So it appears than when lvmetad is gracefully stopped/not running, 
dmeventd correctly resort to device scanning. On the other hand, in the 
previous case, lvmetad was running but returned "Connection refused". 
Should/could dmeventd resort to device scanning in this case also?

> Assuming you've been bitten by this one:
> https://bugzilla.redhat.com/1334063
> possibly? targeted by this commit:
> https://git.fedorahosted.org/cgit/lvm2.git/commit/?id=7ef152c07290c79f47a64b0fc81975ae52554919

Very probable. So, after a LVM update, is best practice to restart the 
machine or at least the dmeventd/lvmetad services?

One more, somewhat related thing: when thin pool goes full, is a good 
thing to remount an ext3/4 in readonly mode (error=remount-ro). But what 
to do with XFS which, AFAIK, does not support a similar 
readonly-on-error policy?

It is my understanding that upstream XFS has some improvements to 
auto-shutdown in case of write errors. Did these improvements already 
tickle to production kernels (eg: RHEL6 and 7)?


Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti at assyoma.it - info at assyoma.it
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