[linux-lvm] question about extending snapshots

[linux-lvm] question about extending snapshots

[Brian Chrisman]

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.
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.

thanks,
Brian

Re: [linux-lvm] question about extending snapshots

[Heinz Mauelshagen]

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?

Yes.

> 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.


Heinz

>
> thanks,
> Brian
>
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