[linux-lvm] Snapshot behavior on classic LVM vs ThinLVM

Gionatan Danti g.danti at assyoma.it
Mon Mar 5 14:27:09 UTC 2018

On 05/03/2018 11:18, Zdenek Kabelac wrote:
> Yes - it has been updated/improved/fixed - and I've already given you a 
> link where you can configure the behavior of XFS when i.e. device 
> reports  ENOSPC to the filesystem.

Sure - I already studied it months ago during my testing. I simply was 
under the impression that dm & xfs teams have different point of view 
regarding the actual status. I'm happy to know that it isn't the case :)

> Well complexity - it might look 'easy' to do on the first sight, but in 
> reality it's impacting all hot/fast paths with number of checks and it 
> would have rather dramatic performance impact.
> The other case is, while for lots of filesystems it might look like best 
> thing - it's not always true - so there are case where it's more desired
> to have still working device with 'several' failing piece in it...
> And 3rd moment is - it's unclear from kernel POV - where this 'full' 
> pool moment actually happens - i.e. imagine running  'write' operation 
> on one thin device and 'trim/discard' operation running on 2nd. device.
> So it's been left on user-space to solve the case the best way -
> i.e. user-space can initiate  'fstrim' itself when full pool case 
> happens or get the space by number of other ways...

Ok, I see.

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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