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Re: [lvm-devel] userspace patches for shared snapshots



On Fri, Feb 26 2010 at  4:17pm -0500,
Mike Snitzer <snitzer redhat com> wrote:

> On Thu, Feb 25 2010 at 11:52pm -0500,
> Mikulas Patocka <mpatocka 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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