Re: 2.6.16.20/dm: can't create more then one snapshot of an lv

[Heinz Mauelshagen <mauelshagen@redhat.com>]

How many snapshots active at once ?
I guess this is a kcopyd scalability issue which needs addressing.

Regards,
Heinz    -- The LVM Guy --

On Tue, Jun 20, 2006 at 10:54:05AM +1000, CaT wrote:
> On Mon, Jun 19, 2006 at 12:00:40PM +1000, CaT wrote:
> > I am attempting to create multiple snapshots of an lv ontop of a raid-5
> > software raid device and ext3+dir_index and resize_inode for the fs.
> > The kernel is a pure 64bit compile with Debian Sarge amd64 running on
> > top of it. The kernel is monolithic and I'm using lvm2 2.01.03-5 with
> > devmapper 1.01.
> > 
> > This works under 2.6.15.7. Under 2.6.16.20 I get this:
> 
> 2.6.17 also fails.
> 
> More info: The failing kernels can deal with multiple pre-created
> snapshots but the moment I try to create one it freezes as below. Mounting
> another snapshotted volume at the time this is frozen freezes mount.
> 
> After reboot the snapshot it froze on making is available to the system
> (though the reboot fails on shutdown as it cannot unmount anything).
> 
> > # lvcreate --snapshot --size 50G --name snap-13 --permission r --verbose /dev/backups/main
> >     Setting chunksize to 16 sectors.
> >     Finding volume group "backups"
> >     Creating logical volume snap-13
> >     Archiving volume group "backups" metadata.
> >     Creating volume group backup "/etc/lvm/backup/backups"
> >     Found volume group "backups"
> >     Loading backups-snap--13
> >     Zeroing start of logical volume "snap-13"
> >     Found volume group "backups"
> >     Removing backups-snap--13
> >     Found volume group "backups"
> >     Found volume group "backups"
> >     Found volume group "backups"
> >     Loading backups-main-real
> >     Loading backups-snap--12-cow
> >     Loading backups-snap--12
> > *freeze*
> 
> -- 
>     "To the extent that we overreact, we proffer the terrorists the
>     greatest tribute."
>     	- High Court Judge Michael Kirby
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Heinz Mauelshagen                                 Red Hat GmbH
Consulting Development Engineer                   Am Sonnenhang 11
Storage Development                               56242 Marienrachdorf
                                                  Germany
Mauelshagen@RedHat.com                            PHONE +49  171 7803392
                                                  FAX   +49 2626 924446
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