[linux-lvm] error creating snapshots

[linux-lvm] error creating snapshots

[Stuart D. Gathman]

Is this a harmless error having to do with some misreported option to notify a
user process when the snapshot is almost full?  Or should I switch backups over
to network based because this means LVM might corrupt data?

CentOS-5.4

# uname -a
Linux xerces.jsconnor.com 2.6.18-164.el5xen #1 SMP Thu Sep 3 04:03:03 EDT 2009 x86_64 x86_64 x86_64 GNU/Linux
# lvcreate -s -L20G -n dmm_snap bms_data/dmm
  bms_data-dmm_snap: event registration failed: 10071:3 
libdevmapper-event-lvm2snapshot.so dlopen failed: 
/usr/lib64/liblvm2cmd.so.2.02: undefined symbol: dm_list_empty
  bms_data/snapshot0: snapshot segment monitoring function failed.
  Logical volume "dmm_snap" created
# echo $?
0
# lvremove bms_data/dmm_snap
Do you really want to remove active logical volume dmm_snap? [y/n]: y
  Logical volume "dmm_snap" successfully removed
# diff /etc/lvm/backup/bms_data /etc/lvm/archive/bms_data_00290.vg
6c6
< description = "Created *after* executing 'lvremove bms_data/dmm_snap'"
---
> description = "Created *before* executing 'lvremove bms_data/dmm_snap'"
13c13
<       seqno = 430
---
>       seqno = 429
235a236,271
> 
>               dmm_snap {
>                       id = "2KshBd-67nj-nyrX-RUKK-LEl2-ZXBP-bJrtwe"
>                       status = ["READ", "WRITE"]
>                       flags = []
>                       segment_count = 1
> 
>                       segment1 {
>                               start_extent = 0
>                               extent_count = 640      # 20 Gigabytes
> 
>                               type = "striped"
>                               stripe_count = 1        # linear
> 
>                               stripes = [
>                                       "pv0", 7648
>                               ]
>                       }
>               }
> 
>               snapshot0 {
>                       id = "zUturd-IQZR-3xYu-SgpB-NnzK-0XKL-JN3fWh"
>                       status = ["READ", "WRITE", "VISIBLE"]
>                       flags = []
>                       segment_count = 1
> 
>                       segment1 {
>                               start_extent = 0
>                               extent_count = 1280     # 40 Gigabytes
> 
>                               type = "snapshot"
>                               chunk_size = 8
>                               origin = "dmm"
>                               cow_store = "dmm_snap"
>                       }

-- 
	      Stuart D. Gathman <stuart@bmsi.com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

[linux-lvm] Re: error creating snapshots

[Mike Snitzer]

On Mon, Nov 02 2009 at 10:35pm -0500,
Stuart D. Gathman <stuart@bmsi.com> wrote:

> Is this a harmless error having to do with some misreported option to notify a
> user process when the snapshot is almost full?  Or should I switch backups over
> to network based because this means LVM might corrupt data?
> 
> CentOS-5.4
> 
> # uname -a
> Linux xerces.jsconnor.com 2.6.18-164.el5xen #1 SMP Thu Sep 3 04:03:03 EDT 2009 x86_64 x86_64 x86_64 GNU/Linux
> # lvcreate -s -L20G -n dmm_snap bms_data/dmm
>   bms_data-dmm_snap: event registration failed: 10071:3 
> libdevmapper-event-lvm2snapshot.so dlopen failed: 
> /usr/lib64/liblvm2cmd.so.2.02: undefined symbol: dm_list_empty
>   bms_data/snapshot0: snapshot segment monitoring function failed.
>   Logical volume "dmm_snap" created

This is harmless but it does mean that dmeventd-based snapshot
usage monitoring is not currently enabled for this snapshot.

But if you restart dmeventd (kill the process and it'll restart next
time you activate the snapshot) it should work.

I'll have a look at how best to cope with this within lvm2 (either
rpm upgrade triggers or...).  But out of curiosity: had you upgraded
lvm2 (lvm2-libs et al) prior to creating the snapshot and dmeventd was
running prior to the upgrade?

Mike

Re: [linux-lvm] Re: error creating snapshots

[Stuart D. Gathman]

On Tue, 3 Nov 2009, Mike Snitzer wrote:

> Stuart D. Gathman <stuart@bmsi.com> wrote:
> 
> > Is this a harmless error having to do with some misreported option to
> > notify a user process when the snapshot is almost full?  Or should I switch
> > backups over
> This is harmless but it does mean that dmeventd-based snapshot
> usage monitoring is not currently enabled for this snapshot.
> 
> But if you restart dmeventd (kill the process and it'll restart next
> time you activate the snapshot) it should work.

Looks like "service lvm2-monitor restart" should do this.  Maybe
the update should restart this service?

> I'll have a look at how best to cope with this within lvm2 (either
> rpm upgrade triggers or...).  But out of curiosity: had you upgraded
> lvm2 (lvm2-libs et al) prior to creating the snapshot and dmeventd was
> running prior to the upgrade?

Yes.  Have not yet rebooted after the update.  Strangely, this doesn't
seem to happen on 32-bit systems at the same update level with the same
update sequence.  

The dmeventd was not restarted with the lvm2 update.  There is some
logic in lvm2-monitor about when stopping dmeventd is dangerous, but
it doesn't seem to think a restart is dangerous.

-- 
	      Stuart D. Gathman <stuart@bmsi.com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

Re: [linux-lvm] Re: error creating snapshots

[Stuart D. Gathman]

On Tue, 3 Nov 2009, Stuart D. Gathman wrote:

> > But if you restart dmeventd (kill the process and it'll restart next
> > time you activate the snapshot) it should work.
> 
> Looks like "service lvm2-monitor restart" should do this.  Maybe
> the update should restart this service?

Nope.  Restarts something, but not dmeventd.

-- 
	      Stuart D. Gathman <stuart@bmsi.com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

Re: [linux-lvm] Re: error creating snapshots

[Stuart D. Gathman]

On Tue, 3 Nov 2009, Mike Snitzer wrote:

> > # lvcreate -s -L20G -n dmm_snap bms_data/dmm
> >   bms_data-dmm_snap: event registration failed: 10071:3 
> > libdevmapper-event-lvm2snapshot.so dlopen failed: 
> > /usr/lib64/liblvm2cmd.so.2.02: undefined symbol: dm_list_empty
> >   bms_data/snapshot0: snapshot segment monitoring function failed.
> >   Logical volume "dmm_snap" created
> 
> This is harmless but it does mean that dmeventd-based snapshot
> usage monitoring is not currently enabled for this snapshot.
> 
> But if you restart dmeventd (kill the process and it'll restart next
> time you activate the snapshot) it should work.

How can restarting a daemon make a library symbol suddenly become defined?
Isn't this a library issue?

-- 
	      Stuart D. Gathman <stuart@bmsi.com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

Re: [linux-lvm] Re: error creating snapshots

[Stuart D. Gathman]

On Tue, 3 Nov 2009, Bryn M. Reeves wrote:

> > > But if you restart dmeventd (kill the process and it'll restart next
> > > time you activate the snapshot) it should work.
> > 
> > How can restarting a daemon make a library symbol suddenly become defined?
> > Isn't this a library issue?
> 
> If the daemon has been running since before the package update it will
> still use the old binary/library images. Killing and re-starting it will
> force it to use the newly updated versions.

Yep, that fixed it.

-- 
	      Stuart D. Gathman <stuart@bmsi.com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

Re: [linux-lvm] Re: error creating snapshots

[Bryn M. Reeves]

On Tue, 2009-11-03 at 11:48 -0500, Stuart D. Gathman wrote:
> On Tue, 3 Nov 2009, Mike Snitzer wrote:
> 
> > > # lvcreate -s -L20G -n dmm_snap bms_data/dmm
> > >   bms_data-dmm_snap: event registration failed: 10071:3 
> > > libdevmapper-event-lvm2snapshot.so dlopen failed: 
> > > /usr/lib64/liblvm2cmd.so.2.02: undefined symbol: dm_list_empty
> > >   bms_data/snapshot0: snapshot segment monitoring function failed.
> > >   Logical volume "dmm_snap" created
> > 
> > This is harmless but it does mean that dmeventd-based snapshot
> > usage monitoring is not currently enabled for this snapshot.
> > 
> > But if you restart dmeventd (kill the process and it'll restart next
> > time you activate the snapshot) it should work.
> 
> How can restarting a daemon make a library symbol suddenly become defined?
> Isn't this a library issue?
> 

If the daemon has been running since before the package update it will
still use the old binary/library images. Killing and re-starting it will
force it to use the newly updated versions.

Regards,
Bryn.