[lvm-devel] lv-shared

[Mike Snitzer]

On Mon, Mar 15 2010 at  4:06pm -0400,
Mikulas Patocka <mpatocka at redhat.com> wrote:

> On Mon, 15 Mar 2010, Mike Snitzer wrote:
> 
> > On Mon, Mar 15 2010 at  3:00pm -0400,
> > Mikulas Patocka <mpatocka at redhat.com> wrote:
> > 
> > > Hi
> > > 
> > > Why did you hide the "lv-shared" volume? With this hidden, the size and 
> > > percentage can't be seen.
> > 
> > You can still see it with: lvs -a
> > 
> > I'll have to revisit why I made it hidden (aside from the fact that the
> > associated DM device is also hidden).  There was some subtle reason that
> > had to do with the refactoring of associations when I eliminated the
> > distinct ->shared_snapshot pointer (otherwise the vg_validate() method
> > would fail).
> 
> I know it can be seen with lvs -a, but I think it's inconvenient for the 
> admin:
> - the admin won't see that there is a shared store taking up space
> - the admin won't see that the origin is a shared snapshot, he sees 'o', 
> but nothing that refers to that 'o'
> - the percentage usage of the shared snapshot is hidden
> 
> I think this information is important and should be displayed with plain 
> "lvs" command without any flags. (for example, the percentage usage is 
> critical, because it can overflow) --- so "lv-shared" shouldn't be hidden.

Sure, not a problem.

I've updated the relevant patch, see:
http://people.redhat.com/msnitzer/patches/multisnap/lvm2/LVM2-2.02.62/lvm-shared-eliminate-shared_snapshot-in-lv.patch

The lib/metadata/metadata.c:snapshot_count() changes in this updated
patch address the vg_validate() issue I was seeing.  The -shared cow was
considered to be a normal "snapshot"; as such the vg_validate() checks
failed.

Mike