On Wed, Jul 26, 2006 at 02:28:53PM +0200, Carsten Otte wrote:
> Very interresting indeed. This pointed me to reading the
> lockfs/unlockfs semantics in Linux, and I think I need to withdraw my
> statement regarding flashcopy snapshots: because of the fact that
> there is no lockfs/unlockfs interaction when doing flashcopy, and
> because of dirty pages in the page cache during snapshot, flashcopy
> will not generate a consistent snapshot. Therefore, using flashcopy on
> an active volume from outside Linux is _not_ suitable for backup purposes.
>
> The only feasible way to get a consistent snapshot is to use
> dm-snapshot from within Linux. This snapshot copy can later on be used
> with a backup feature outside Linux.

If you use xfs you can also put the filesystem in frozen state from
userspace with the xfs_freeze utility.  I know of inhouse backup tools
at various companies that make use of this feature.

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