Re: [linux-lvm] mounting snapshot errors

[Chris Beck <cbeck gene concordia ca>]

Yah, I saw some stuff about this in the LVM-HOWTO:

http://tldp.org/HOWTO/LVM-HOWTO/snapshots_backup.html

| If the snapshot is of an XFS filesystem, the xfs_freeze command should 
be used to quiesce the filesystem before creating the snapshot. (if the 
filesystem is mounted) |

|# xfs_freeze -f /mnt/point; lvcreate -L592M -s -n dbbackup /dev/ops/databases; xfs_freeze -u /mnt/point 

If you are using XFS as the filesystem you will need to add the nouuid option to the mount command:

# mount /dev/ops/dbbackup /mnt/ops/dbbackup -onouuid,ro
              
Previously, the norecovery option was suggested to allow the mounting of XFS snapshots.
It has been recommended not to use this option, but to instead use xfs_freeze to quiesce the filesystem before creating the snapshot.

|

cheers,
chris


It is whispered that Greg Freemyer was heard, on or about 1/28/2004 
12:34 PM to say:

> On Wed, 2004-01-28 at 02:28, R Dicaire wrote:
>  
>
> > On Tue, 2004-01-27 at 21:53, Little, Chris wrote:
> >    
> >
> > > is the filesystem you are snapshotting still mounted when you execute the
> > > snapshot?  They need to be offline before the snapshot takes place.
> > >      
> > Yes, they are still mounted when I take a snapshot, I must have missed that
> > in the docs, that in itself poses a problem as I then cant umount the volumes
> > without killing services. I'd understood the snapshotting process as being
> > able to snapshot a live filesystem, and then mount the snapshot to perform
> > backups from it instead of the live filesystem. Whats the purpose of the
> > --size arg to lvcreate when taking a snapshot, I thought it was a buffer
> > to hold data that'd normally be written to disk but cant when the
> > snapshot exists? I'm confused.
> >
> >    
> I snapshot live mounted volumes every day.  (LVM 1.x, kernel 2.4.21)
>
> It works.
>
> I use xfs.
>
> For LVM snapshot to work with mounted filesystems you either have to
> have the vfs-lock patch applied or invoke a filesystem freeze from user
> space prior to creating the snapshot.
>
> With xfs, I use the xfs_freeze command from userspace.
>
> Then on the xfs mount, I have to use the "-o ro,nouuid" flag to mount
> the snapshot because the master volume and the  snapshot have the same
> uuid.
>
> Greg
>  

--
Chris Beck / Y.A.B.A. / Fungal Genomics
CFSG / Concordia University
"La loi dans sa majestueuse égalité, interdit à tous, aux riches comme
aux pauvres de dormir sous les ponts, de coucher dans la rue et de voler
du pain." -- Anatole France (Les Lys Rouge - 1894)