Dne 16. 11. 22 v 15:38 Gionatan Danti napsal(a):
Il 2022-11-16 11:50 Zdenek Kabelac ha scritto:
Well - as said - vg on vg is basically equivalent of the original LV
on top of VDO manager.
Hi Zdenek,
it seems clunkier to manage two nested VG/LV if you ask me.
IMHO not different from lvm on top of vdo managed volume.
It should be mostly equal (and in few cases possibly even easier or at least
more OS friendly)
But still these fast snapshot do not solve you a problem of double
out-of-space fault.
Yeah, but available space requires constant monitor even when dealing with
lvmthin.
It's good for experimenting - but I'd not suggest to use this setup.
In RHEL7 it was specifically supported - see here[1]:
"As a general rule, you should place certain storage layers under VDO and
others on top of VDO:
Under VDO: DM-Multipath, DM-Crypt, and software RAID (LVM or mdraid).
On top of VDO: LVM cache, LVM snapshots, and LVM Thin Provisioning"
For a practical example: in the past I experimented with a storage stack
composed of raid -> vdo -> lvmthin -> xfs serving qemu/kvm virtual disk files.
The lvmthin layer enabled rolling snapshots, and was a key feature of the test
setup.
Now the only method to replicate that is to have two nested LVM instances, one
running vdo and one lvmthin - right?
Well - it's not difficult 'coding' to enable using 'VDO LV' as thinpool data
LV, however we currently lack a lot on support for 'VDO LV' recovery alone in
lvm2 - so until this will get polished - we try to avoid shot ourself to our
foots with enabling these complicated stacks ATM :)
We also have some ideas for different snapshoting inside VDO - so we will see
how that will go - it looks more supportable then combining VDO+THIN together.
Regards
Zdenek
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