Re: LVM Snapshot Feature

[Mikulas Patocka <mpatocka@redhat.com>]

On Fri, 1 Aug 2008, Adam Hamsik wrote:

> On Aug,Friday 1 2008, at 9:35 AM, Bombardier, Pascal wrote:
> 
> > Hi,
> > 
> > In your opinion, does it make sense to be able to create non-persistent
> > snapshots ?
> > In the case of a filesystem backup, a non-persistent snapshot would be a
> > snapshot that we agree to lose in case of failure or reboot. If anything
> > happens, a server administrator would have to recreate a new snapshot
> > and then restart the backup.
> > In this case, I think metadata could be stored in memory instead of on
> > disk, which should improve LVM snapshot performance.
> > 
> > Is this theory wrong, and is this something which can be implemented
> > easily in the current LVM code ?
> > 
> 
> AFAIK non-persistent snapshots are already implemented see
> DM_PERSISTENT_DEV_FLAG ? I haven't look at linux kernel code how is
> it done but when I solve my lvcreate -s bug on NetBSD non-persistent
> snapshots are next :).
> 
> Regards
> 
> Adam.

Yes. They are implemented in device mapper in kernel --- but no userspace 
lvm tool can use them. You can only create them using dmsetup.

Mikulas