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

[Zdenek Kabelac]

Dne 15. 11. 22 v 23:41 Gionatan Danti napsal(a):
> 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?

Well - as said - vg on vg is basically equivalent of the original LV on top of 
VDO manager.

But still these fast snapshot do not solve you a problem of double 
out-of-space fault.

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

It's good for experimenting - but I'd not suggest to use this setup.

Regards

Zdenek