[Lustre-discuss] e2scan for backup

[Kalpak Shah]

On Thu, 2008-03-13 at 13:48 +0100, Brian J. Murrell wrote:
> On Thu, 2008-03-13 at 12:59 +0100, Jakob Goldbach wrote:
> > 
> > No need to freeze the filesystem while creating the snapshot to ensure a
> > consistent filesystem on the snapshot ?
> 
> I've been corrected about this before and maybe it will happen again,
> but a) there is no need to freeze the filesystem and b) probably when
> you mount the snapshot, the journal (which may contain transactions when
> the snapshot is taken) will be replayed and then everything should be
> good.

For taking snapshots the filesystem(or block device) must be frozen or
the snapshots will not be consistent. LVM calls freeze_bdev() to lock a
filesystem and bring it into a consistent state. It is not exported to
userspace though and is currently uses only by device-mapper AFAIK.

Thanks,
Kalpak.

> 
> > (xfs has a xfs_freeze function that does just this)
> 
> Yeah.  I don't know enough about xfs to understand why this is needed,
> but probably the inconsistency of an "open" xfs filesystem is more
> disastrous than an ext3 filesystem.
> 
> b.
> 
> 
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