[linux-lvm] lvm-vdo, snapshots and cache

[Gionatan Danti]

Il 2022-11-15 22:56 Zdenek Kabelac ha scritto:
> You could try  'vg' on top of another 'vg' - however I'd not recommend
> to use it this way (and it's unssuported (&unsupportable) by lvm2 in
> general)

Hi Zdenek,
yeah, I would strongly avoid that outside lab testing.

> IMHO I'd not recommend to combine 2 provisioning technologies - it's
> already hard to resolve 'out-of-space' troubles with just one
> technology...

The issue is that fast snapshots are only provided by dm-thin, meaning 
that lvmthin is almost mandatory for implementing a rolling/continuous 
snapshot scheme. And, on a more basic level, if we can not stack LVM on 
top of a VDO LV (in a supported manner), how can we take a snapshot of 
user data residing on that specific volume?

This seems a clear regression vs a separate VDO device. Am I missing 
something?

> Caching should be already support - on VDO LV as well as on VDOPOOL LV
> (both work somewhat differently).

Good, thanks for confirming. I will do some tests...
Regards.

-- 
Danti Gionatan
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