[linux-lvm] mounting snapshot errors

Greg Freemyer freemyer-ml at NorcrossGroup.com
Wed Jan 28 12:48:01 UTC 2004

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

Greg Freemyer

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