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

Gionatan Danti g.danti at assyoma.it
Tue May 17 13:09:38 UTC 2016

> Well yeah - ATM we rather take 'early' action and try to stop any user
> on overfill thin-pool.

It is a very reasonable standing

> Basically whenever  'lvresize' failed - dmeventd plugin now tries
> to unconditionally umount any associated thin-volume with
> thin-pool above threshold.
> For now  -  plugin   'calls'  the tool - lvresize --use-policies.
> If this tool FAILs for ANY  reason ->  umount will happen.
> I'll probably put in 'extra' test that 'umount' happens
> with  >=95% values only.
> dmeventd  itself has no idea if there is configure 100 or less - it's
> the lvresize to see it - so even if you set 100% - and you have enabled
> monitoring  - you will get umount (but no resize)

Ok, so the "failed to resize" error is also raised when no actual resize 
happens, but the call to the "dummy" lvresize fails. Right?

> If you strictly don't care about any tracing of thin-pool fullness,
> disable  monitoring in lvm.conf.

While this thin pool should never be overfilled (it has a single, 
slightly smaller volume with no snapshot in place) I would really like 
to leave monitoring enabled, as it can prevent some nasty suprises (eg: 
avoid pool overfilling by a snapshot that is "forgotten" and never removed).

> Well 'lvmetad' shall not crash, ATM this may kill commands - and further
> stop processing - as we rather 'stop' further usage rather than allowing
> to cause bigger damage.
> So if you have unusual system/device setup causing  'lvmetad' crash -
> open BZ,
> and meawhile  set   'use_lvmetad=0' in your lvm.conf till the bug is fixed.

My 2 cents are that the last "yum upgrade", which affected the lvm 
tools, needed a system reboot or at least the restart of the lvm-related 
services (dmeventd and lvmetad). The strange thing is that, even if 
lvmetad crashed, it should be restartable via the lvm2-lvmetad.socket 
systemd unit. Is this a wrong expectation?


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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