[linux-lvm] Failed merge, still running?

[Mauricio Tavares]

On Wed, Jan 22, 2020 at 8:12 AM Zdenek Kabelac <zkabelac at redhat.com> wrote:
>
> Dne 22. 01. 20 v 11:58 Mauricio Tavares napsal(a):
> > So after a botched package update I decided to revert to the snapshot
> > I took just before doing the update. After shutting guest down, I
> > started
> >
> > lvconvert --merge vmhost_vg0/desktop_snap_20200121
> >
> > and instead of seeing the usual percentage of how far it has
> > completed, I got nothing. lvs -a -o +devices shows
> >
> >    LV                      VG         Attr       LSize  Pool Origin
> > Data%  Meta%  Move Log Cpy%Sync Convert Devices
> >    desktop                 vmhost_vg0 Owi-a-s--- 20.00g
> >                                       /dev/sdb3(14848)
> >    [desktop_snap_20200121] vmhost_vg0 Swi-a-s--- 10.00g      desktop 100.00
> >
> > I see nothing when I do lsof against both the lv (lsof
> > /dev/vmhost_vg0/desktop) and its snapshot. dmsetup tells me:
> >
> > [root at vmhost ~]# dmsetup info /dev/vmhost_vg0/desktop
> > Name:              vmhost_vg0-desktop
> > State:             ACTIVE
> > Read Ahead:        256
> > Tables present:    LIVE
> > Open count:        0
> > Event number:      0
> > Major, minor:      253, 5
> > Number of targets: 1
> > UUID: LVM-qa4WnlE7w8V7pasHwdNH6bnpz2ajYY1F2ZXwTWzpUE2r6eE2DftMGLHdeATE8XAq
> >
> > [root at vmhost ~]# dmsetup info /dev/vmhost_vg0/desktop_snap_20200121
> > Name:              vmhost_vg0-desktop_snap_20200121
> > State:             ACTIVE
> > Read Ahead:        256
> > Tables present:    LIVE
> > Open count:        0
> > Event number:      0
> > Major, minor:      253, 15
> > Number of targets: 1
> > UUID: LVM-qa4WnlE7w8V7pasHwdNH6bnpz2ajYY1FkyXcvv8ai1Sc0q5zlsXeenYOqCPUXs3M
> >
> > [root at vmhost ~]#
> >
> > Before I blow that lv up, what else should I be checking?
>
>
> Hi
>
>
> Merging can ONLY start when devices are not in-use - so if you've issued merge
> command while devices were still opened - the 'merge' operation has
> been just committed into lvm2 metadata and the actual merge would normally
> happen/start with next activation of the merged LV.
>
      Interesting. I guess when I told guest to shutdown I did not
wait for it to be completely shutdown as far as kvm was concerned; it
might have been doing some housekeeping when I unleashed lvconvert.

> You can invoke it also by issuing 'lvchange --refresh' which may start to
> merging (if the conditions do allow the operation to start).
>
      Thanks! As soon as I ran

lvchange --refresh vmhost_vg0/desktop

I was able to see progress:

[root at vmhost ~]# lvs -a -o +devices
[desktop_snap_20200121] vmhost_vg0 Swi-a-s--- 10.00g      desktop 30.78
[desktop_snap_20200121] vmhost_vg0 Swi-a-s--- 10.00g      desktop 30.76
[...]

After a few more minutes, the vm gues was "rewinded." Now I can run it again.

Thanks again!

> Regard
>
> Zdenek
>
>