[linux-lvm] question about extending snapshots

Heinz Mauelshagen heinzm at redhat.com
Mon Jan 7 13:27:15 UTC 2013

On 01/05/2013 01:00 AM, Brian Chrisman wrote:
> I'm running rhel6.2 nearly stock.
> When I mount a snapshot (writable) and perform an lvextend, the CoW
> table increases in size, but the logical volume size (for example,
> blockdev output) doesn't change itself.

You deploy more COW space to allow for a larger change set either 
applied to the origin or the snapshot or both doing so, yes.

_But_ snapshots always have origin size.

> Is this impossible because the regions of the snapshot volume wouldn't
> have any corresponding regions in the origin volume?


> Is there any way to change the size reported by a snapshot?
> What I'm trying to do is take a snapshot, mount it, do stuff to it,
> and if I need, make it bigger, and if I need to, just drop it and
> create a new one.
> If I just take a snapshot and modify the origin and use a merge, then
> space becomes an issue.

Watch new snapshots and thin provisioning, which'll help the space issue 
in future RHEL and existjng upstream dm/lvm releases.


> thanks,
> Brian
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