[Ocfs2-users] Can't delete LV snapshot after mounting

[Armin Wied]

Yes, LVM and MD are local.

Thank's a lot - decrementing the ref works!

After unmounting
ocfs2_hb_ctl -I -d /dev/vg00/lv00snap o2cb
shows 1 refs.

After decrementing, it shows 0 refs, the corresponding o2hb thread
disappears and I can remove the snapshot.

Is it safe to do so or might there be any potential dangerous side effects?

Best regards
Armin


> -----Original Message-----
> From: Sunil Mushran [mailto:sunil.mushran at oracle.com]
> Sent: Friday, March 19, 2010 5:32 PM
> To: Armin Wied
> Cc: ocfs2-users at oss.oracle.com
> Subject: Re: [Ocfs2-users] Can't delete LV snapshot after mounting
>
>
> ok so lvm, md are local to a node.
>
> It should be stopping on umount. If not, try to shut it manually.
>
> To see the number of refs, do:
> # ocfs2_hb_ctl -I -d /dev/sdX o2cb
>
> To decrement a ref, do:
> # ocfs2_hb_ctl -K -d /dev/sdX o2cb
>
> The fs decrements using UUID.
> # ocfs2_hb_ctl -K -u UUID o2cb
>
> To find the uuid, do:
> tunefs.ocfs2 -Q "%U\n" /dev/sdX
>
> Armin Wied wrote:
> > Dear Sunil
> >
> > Thank's a lot for your reply.
> >
> > I think I maybe wasn't clear enough on one point and you got me wrong.
> > I don't have LVM on top of DRBD but the other way round:
> > OCFS2 -> DRBD -> LVM -> MD-RAID -> physical disk
> > Same on both machines, so do you still think, that's queasy?
> >
> > I have used iSCSI already for some other setup, but wanted to use just 2
> > single PCs for this setup to have a cluster system with no
> single point of
> > failure, so I don't see any advantage of using iSCSI in this scenario.
> >
> > You are right with your guess reagrding the o2hb thread. There
> is one after
> > the system is rebootet and a second one is started, as soon as
> I mount the
> > snapshot. After unmounting, both are still there, so that
> appears to be the
> > reason, why I can't remove the snapshot.
> >
> > Is there any (safe) way get rid of it after unmounting?
> >
> > Thank's
> > Armin
> >
> >
> >
> >
> >> -----Original Message-----
> >> From: Sunil Mushran [mailto:sunil.mushran at oracle.com]
> >> Sent: Thursday, March 18, 2010 6:28 PM
> >> To: Armin Wied
> >> Cc: ocfs2-users at oss.oracle.com
> >> Subject: Re: [Ocfs2-users] Can't delete LV snapshot after mounting
> >>
> >>
> >> I am queasy recommending such a setup to anyone. It is one
> thing to handle
> >> a workload. The problem is about handling user/admin errors. You are
> >> essentially
> >> running a local volume manager that is unaware of the other node. Any
> >> reconfig
> >> that is not coordinated will lead to corruption. Below that you have
> >> drbd which
> >> a fine block device replication solution. But I would personally choose
> >> iscsi
> >> which is a excellent lowcost shared device. Also, does not limit you to
> >> 2 nodes.
> >> The iscsi target in sles is known to be good. Why not just use that and
> >> use drbd
> >> to replicate the device (like emc srdf) for still higher availability.
> >>
> >> Having said that, the 2 you are seeing is not because of the number of
> >> nodes but
> >> because of the hb thread. umount is supposed to stop that hb thread.
> >> Maybe that is
> >> not happening.
> >>
> >> # ps aux | grep o2hb
> >> You should see one when the volume is mounted and not when umounted.
> >>
> >> Sunil
> >>
> >> Armin Wied wrote:
> >>
> >>> Hello group!
> >>>
> >>> I'm pretty new to ocfs2 and clustered file systems in general.
> >>> I was able to set up a 2 node cluster (CentOS 5.4) with ocfs2
> >>>
> >> 1.4.4 on DRBD
> >>
> >>> on top of a LVM volume.
> >>>
> >>> Everything works like a charm and is rock solid, even under heavy load
> >>> conditions, so I'm really happy with it.
> >>>
> >>> However, there remains one little problem: I'd like to do backups with
> >>> snapshots. Creating the snapshot volume, mounting, copying and
> >>>
> >> dismounting
> >>
> >>> works like expected. But I can't delete the snapshop volume
> after it was
> >>> mounted once.
> >>>
> >>> What I do is:
> >>>
> >>> lvcreate -L5G -s -n lv00snap /dev/vg00/lv00
> >>> tunefs.ocfs2 -y --cloned-volume /dev/vg00/lv00snap
> >>> mount -t ocfs2 /dev/vg00/lv00snap /mnt/backup
> >>>
> >>> (copy stuff)
> >>>
> >>> umount /mnt/backup
> >>> lvremove -f /dev/vg00/lv00snap
> >>>
> >>> lvremove fails, saying, that the volume is open. Checking with
> >>>
> >> lvdisplay it
> >>
> >>> tells me "# open" is 1.
> >>> And that's the funny thing: After creating the snapshot volume,
> >>>
> >> # open is 0,
> >>
> >>> what's not a surprise. After mounting the volume, # open is 2 -
> >>>
> >> which is the
> >>
> >>> same for the other ocfs2 volume and makes sense to me, as there
> >>>
> >> are 2 nodes.
> >>
> >>> But after unmounting the snapshot volume, the number decreases
> >>>
> >> to 1, not to
> >>
> >>> 0 so LVM consideres the volume still open.
> >>>
> >>> I also tried mounting read only and/or adding "--fs-features=local" to
> >>> tunefs.ocfs2 without success. In the moment I have to reboot
> >>>
> >> the node to be
> >>
> >>> able to remove the snapshot.
> >>>
> >>> So what am I doing wrong?
> >>>
> >>> Thank's a lot for any hint!
> >>>
> >>> Armin
> >>>
> >
> >
> >
>
>