Re: pvmove thin volume doesn't move

[Zdenek Kabelac <zdenek.kabelac@gmail.com>]

Dne 19. 11. 25 v 0:14 Brian J. Murrell napsal(a):
> On Tue, 2025-11-18 at 00:37 +0100, Zdenek Kabelac wrote:
>>
>>
>> Hi
> 
> Hi!
> 
>> You can always create 'new LV' on the PV you prefer to use and then
>> with good
>> old 'dd'  command copy deviceA->deviceB - preferably while device
>> your are
>> copying is not in use (i.e. if you are copying LV which holds your
>> filesystem
>> - the partition should not be mounted) - once all your data are
>> copied you
>> just reconfigure fstab to mount different new LV.
> 
> Yes, indeed, of course that is one way.  And I do appreciate the effort
> of you taking the time to suggest that.  But not having to do these
> kinds of off-line bulk data copy operations is one of the major
> attractions of LVM.  Once we have to start reverting back to the more
> cumbersome and interrupting methods the added complexity of LVM starts
> to lose it's attraction and value.
> 
>> lvm2 does not (ATM) support this kind of operation.
> 
> Pity that one has to choose between efficient space use and efficient
> snapshots or being able to migrate data live but cannot have both.  :-(
> 
> Is being able to do this on the roadmap at least or will this always
> remain a fundamental limitation?

Hi

Well AFAIK you are 'lonely' person wanting this.
Usually once user goes with thin-pools - it's decision taken with knowledge 
that the only way out is to take out whole data out of thin-pool and copy them 
to the new place - there is obviously no point on 'picking individual 
thin-chunks out of thin-pool - move them out of thin-pool and reshuffling 
whole thin-pool (and thin-chunks are i.e. 64K while our extents are typical >4M)

So if user wants to 'accelerate' usage of thin-pool (if they still use archaic 
hdd) - they can always cache thin-pool data volume as such on SSD/nvme - 
giving performance boost to the whole thin-pool usage.

So ATM this feature is not really on the roadmap - although there would be 
probably not too complicated path of allowing to 'install' raid on thin LV - 
let the raid do its mirroring and then split raid and eventually drop thinLV 
relaxing the space in thin-pool - I think there was some effort already made 
towards this LV conning support - but it's low on the priority list.


Regards

Zdenek