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Re: [linux-lvm] mounting snapshot errors

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


| 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.



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


-- 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)

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