[linux-lvm] Snapshotting concatenated devices.

[Jay Weber]

Yep, it's not the same issue though.  fsck will return that it's not a
valid fs, bad magic, etc.  The created snapshot device just doesn't seem
to have the proper pointers until I shutdown the VG, restart it and
manipulate the snapshot device before any other devices on the VG.

On Tue, 22 May 2001, Austin Gonyou wrote:

> Date: Tue, 22 May 2001 15:25:02 -0500 (CDT)
> From: Austin Gonyou <austin at coremetrics.com>
> Reply-To: linux-lvm at sistina.com
> To: linux-lvm at sistina.com
> Subject: Re: [linux-lvm] Snapshotting concatenated devices.
>
> Have you tried to fsck that fs? It sounds like a similar problem I'm
> having with resizing volumes and XFS. It's not an XFS issue, a single
> drive resize with xfs_growfs works fine, but when resizing a volume to
> make it bigger, then trying to grow the FS, I get a FS corrupted
> error.(990). That said, running xfs_repair FS shows that the superblock is
> in a different place and it repairs it and I can move on.
>
> --
> Austin Gonyou
> Systems Architect, CCNA
> Coremetrics, Inc.
> Phone: 512-796-9023
> email: austin at coremetrics.com
>
> On Tue, 22 May 2001, Jay Weber wrote:
>
> > Hi folks,
> >
> > Here's an odd one for you.  When using concatenated logical volumes (an
> > LV that consists of multiple PVs in the VG) snapshots don't appears to be
> > proper after they are taken.  It doesn't generate any errors when the
> > snapshot is performed.  But, if you dumpe2fs or attempt to mount the
> > snapshot it doesn't see the filesystem superblock, etc.
> >
> > To expand on this a bit further, the above isn't always true.  It only
> > seems to occur when I use a larger volume which uses larger extent sizes.
> > The larger volume in total consists of about 400G in the VG.  So, for
> > example, I create an LV of 350G and leave myself 50G for snapshot
> > purposes.
> >
> > It does work properly for me using my memorystick, which is a total of 16M
> > and I use an extent size of 1M.
> >
> > In both cases I just make two partitions on the underlying device and
> > concat them into the one VG.
> >
> > Lastly, in the case where snapshots aren't readable after being created,
> > there is one step of events I can perform to make the snapshot usable
> > again.  It consists of:
> >
> > 	umount the LV
> > 	vgchange -an VG
> > 	vghcnage -ay VG
> > 	mount the snapshot of the LV first
> > 	then mount the LV
> >
> > If I mount the LV first though, I end up with the unusable snapshot again.
> > In the above example after the snapshot is mounted, it appears to look
> > okay and appears to be functioning (COW, etc) properly.
> >
> > Any ideas?
> >
> > I haven't seen this occur on non concattenated devices.  We also seem to
> > have this issue when using striped devices.
> >
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> >
>
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