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
