Dne 14.9.2015 v 21:16 Chris Friesen napsal(a):
On 09/14/2015 12:47 PM, Zdenek Kabelac wrote:
Dne 14.9.2015 v 20:05 Chris Friesen napsal(a):
Hi,
I'm running a 3.10 kernel with LVM 2.02.95.
I'm running into a problem where activating snapshots can take quite a long
time, roughly one minute per 25GB of delta between the snapshot and the origin
volume. (See below for my test procedure.)
I realize that my kernel/LVM aren't exactly bleeding edge, and I wondering
whether more recent versions have done anything to speed up the activation
process (like maybe making it more lazy-loaded rather than reading in a bunch
of data up-front).
If anyone is aware of such improvements, I'd appreciate it if you could point
me at the appropriate changes.
Hi
There is NO way to accelerate your existing setup, other then placing delta on
SSD - the format of snapshot was meant to be used 'temporarily' - i.e. until
you
take backup of LV - but not for long-term multi-gigabyte case.
This is major mis-use of this 'snapshot' feature - which repeats over and
over...
If you want to use long-living snapshots - you need to use thin-provisioning,
Thanks for the quick response.
Presumably we would still have multi-GB of delta between the original volume
and the snapshot, so what would make the activation of a thin-provisioned
snapshot faster? Is the metadata stored differently?
Yes - metadata are on separate device(LV) and are using b-trees.
So now you could i.e. chain snap-of-snap-of-snap...
Also snaps do not need to be active with origin and many other goodies.
Drawbacks - all data have to be in same pool and share same space,
so you can't run 'just' 'snapshot' out-of-space - whole pool is out-of-space.
Also min chunk size is 64K (instead of 4K for old-snap)
Anyway - try and play and see what performs better and suit your needs.
Zdenek
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