[lvm-devel] userspace patches for shared snapshots
Mike Snitzer
snitzer at redhat.com
Wed Mar 3 22:37:40 UTC 2010
On Fri, Feb 26 2010 at 4:17pm -0500,
Mike Snitzer <snitzer at redhat.com> wrote:
> On Thu, Feb 25 2010 at 11:52pm -0500,
> Mikulas Patocka <mpatocka at redhat.com> wrote:
> > > # lvs
> > > LV VG Attr LSize Origin Snap% Move Log Copy% Convert
> > > testlv1 test owi-a- 4.00g
> > > testlv1-shared test swi--- 1.00g testlv1 100.00
> > >
> > > NOTE: strikes me as odd that the testlv1-shared Snap% is 100%. I've
> > > fixed the same with the snapshot-merge code before; will dig deeper in a
> > > bit.
> >
> > This is actually bug in the kernel, it starts with the smallest possible
> > size and extends the internal data structures when the first operation is
> > performed. So, if you ask for status without performing any operation, it
> > reports 100%.
> >
> > Thanks for finding it, I overlooked it. I'l fix that.
>
> Sure, I'll be interested to see your fix. I'm not clear on what you're
> referring to.
BTW, the patches I posted earlier change this behaviour, in particular
this patch:
http://people.redhat.com/msnitzer/patches/multisnap/lvm2/LVM2-2.02.62/lvm-shared-eliminate-shared_snapshot-in-lv.patch
Now the -shared store is hidden:
# lvs
LV VG Attr LSize Origin Snap% Move Log Copy% Convert
testlv1 test owi-a- 4.00g
# lvs -a
LV VG Attr LSize Origin Snap% Move Log Copy% Convert
testlv1 test owi-a- 4.00g
[testlv1-shared] test swi--- 1.00g testlv1 0.00
You'll also note that Snap% is no longer 100%
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