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

[Gionatan Danti <g.danti@assyoma.it>]

Hi list,
I had an unexptected filesystem unmount on a machine were I am using 
thin provisioning.

It is a CentOS 7.2 box (kernel 3.10.0-327.3.1.el7, 
lvm2-2.02.130-5.el7_2.1), with the current volumes situation:
# lvs -a
   LV                   VG         Attr       LSize  Pool         Origin 
Data%  Meta%  Move Log Cpy%Sync Convert
   000-ThinPool         vg_storage twi-aotz-- 10.85t                     
74.06  33.36
   [000-ThinPool_tdata] vg_storage Twi-ao---- 10.85t
   [000-ThinPool_tmeta] vg_storage ewi-ao---- 88.00m
   Storage              vg_storage Vwi-aotz-- 10.80t 000-ThinPool        
74.40
   [lvol0_pmspare]      vg_storage ewi------- 88.00m
   root                 vg_system  -wi-ao---- 55.70g
   swap                 vg_system  -wi-ao----  7.81g

As you can see, thin pool/volume is at about 75%.

Today I found the Storage volume unmounted, with the following entries 
in /var/log/message:
May 15 09:02:53 storage lvm[43289]: Request to lookup VG vg_storage in 
lvmetad gave response Connection reset by peer.
May 15 09:02:53 storage lvm[43289]: Volume group "vg_storage" not found
May 15 09:02:53 storage lvm[43289]: Failed to extend thin 
vg_storage-000--ThinPool-tpool.
May 15 09:02:53 storage lvm[43289]: Unmounting thin volume 
vg_storage-000--ThinPool-tpool from /opt/storage.
...

The lines above repeated each 10 seconds.

What puzzle me is that both thin_pool_autoextend_threshold and 
snap_pool_autoextend_threshold are disabled in the lvm.conf file 
(thin_pool_autoextend_threshold = 100 and snap_pool_autoextend_threshold 
= 100). Moreover, no custom profile/policy is attached to the thin 
pool/volume.

To me, it seems that the lvmetad crashed/had some problems and the 
system, being "blind" about the thin volume utilization, put it offline. 
But I can not understand the "Failed to extend thin 
vg_storage-000--ThinPool-tpool", and I had *no* autoextend in place.

I rebooted the system and the Storage volume is now mounted without 
problems. I also tried to write about 16 GB of raw data to it, and I 
have no problem. However, I can not understand why it was put offline in 
the first place. As a last piece of information, I noted that kernel & 
lvm was auto-updated two days ago. Maybe it is related?

Can you give me some hint of what happened, and how to avoid it in the 
future?
Thanks.

-- 
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8