[linux-lvm] Reserve space for specific thin logical volumes
g.danti at assyoma.it
Wed Sep 13 08:28:20 UTC 2017
Il 13-09-2017 10:15 Zdenek Kabelac ha scritto:
> Ohh this is pretty major constrain ;)
Sorry for not explicitly stating that before.
> But as pointed out multiple times - with scripting around various
> fullness moments of thin-pool - several different actions can be
> programmed around,
> starting from fstrim, ending with plain erase of unneeded snapshot.
> (Maybe erasing unneeded files....)
> To get most secure application - such app should actually avoid using
> page-cache (using direct-io) in such case you are always guaranteed
> to get exact error at the exact time (i.e. even without journaled
> mounting option for ext4....)
True, but pagecache exists for a reason. Anyway, this is not anything
you can "fix" in device mapper/lvm, I 100% agree with that.
> Partially this might get solved in 'some' cases with fully provisioned
> thinLVs within thin-pool...
> What comes to my mind as possible supporting solution is -
> adding possible enhancement on LVM2 side could be 'forcible' removal
> of running volumes (aka lvm2 equivalent of 'dmsetup remove --force')
> ATM lvm2 prevents you to remove 'running/mounted' volumes.
> I can well imagine LVM will let you forcible replace such LV with
> error target - so instead of thinLV - you will have single 'error'
> target snapshot - which could be possibly even auto-cleaned once the
> volume use-count drops bellow 0 (lvmpolld/dmeventd monitoring
> (Of course - we are not solving what happens to application
> using/running out of such error target - hopefully something not
> completely bad....)
> This way - you get very 'powerful' weapon to be used in those
> so you can drop uneeded volumes ANYTIME you need to and reclaim its
This would be *really* great. I played with dm-setup remove/error target
and, while working, it often freezed LVM.
An integrated forced volume removal/swith to error target would be
Assyoma S.r.l. - www.assyoma.it
email: g.danti at assyoma.it - info at assyoma.it
GPG public key ID: FF5F32A8
More information about the linux-lvm