Re: [linux-lvm] Testing ThinLVM metadata exhaustion

[Gionatan Danti <assistenza@assyoma.it>]

> 
> bugzilla.redhat.com
> 
> Anyway - 6.8 will likely be your solution.
> 
> Thin-provisioning is NOT supposed to be used at 'corner' cases - we
> improve them, but older version simply had more of them as there was
> always clearly communicated do not over-provision if you can't provide
> the space.
> 
> Out-of-space  is not equal if you run out of your filesystem space -
> you can't expect things will continue to work nicely - the cooperation
> of block layer with filesystem and metadata resilience are continually
> improved.
> 
> We have actually even seen users 'targeting' to hit full-pool as a
> part of regular work-flow - bad bad plan...
> 
> Regards
> 
> Zdenek

Hi Zdenek,
thanks for your courtesy.

I absolutely agree with you that in no case metadata exhaustion can be 
considered part of a "regular work-flow". At the same time, I often do 
"stress test" specifically crafted to put the software/hardware in the 
worst possible condition. In this manner, should an exceptionally bad 
situation occour, I know how to deal with it.

I have another question: does this bug only happen when metadata space 
is exausted? I am asking this because searching for other peoples with 
the same error message, I read this bug report: 
http://www.redhat.com/archives/dm-devel/2014-March/msg00021.html

The bug described in the message above does not necessarily happen at 
metadata exaustion time, as confirmed here: 
https://bugzilla.kernel.org/show_bug.cgi?id=68801

I understand that these are old (2014) bugs and that were fixed in Linux 
3.14 but, using thin LVM volumes in production systems (albeit with RH 7 
only), I want to be reasonably sure that no show-stopper bug can hit me. 
Are current RH OSes (6.7 and 7.2) immune from this bug (metadata 
corruption even if tmeta is not full)?

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