Re: [Evms-devel] newbie question - cannot mount snapshot volume

[Tony S. <to...@pe...>]

Hi Chia,

I've seen this before when trying to mount a read-only snapshot of a 
journalled filesystem (in my case ReiserFS). When you mount a journalled FS, 
the journal may need to be replayed to recover the FS to a consistent point 
and that's not possible on a read-only medium. 

So:

(a) snapshots of journalled filesystems should be created as writable
(b) you can use "mount -o ro" to mount the snapshot filesystem read-only. 

That will allow the snapshot to be writable so the journal can be replayed, 
but will prevent users from updating the mounted filesystem.

Tony

> On Monday 22 September 2003 19:44, Chia Chao wrote:
> > Hi
> >
> > I created a snapshot volume but attempts to mount this volume resulted in
> > error:
> >
> > Engine: mount: mount: block device /dev/evms/sv is write-protected,
> > mounting red-only
>
> This just means you created the snapshot as read-only instead of writeable.
>
> > mount: wrong fs type, bad option, bad superblock on /dev/evms/sv, or too
> > many mounted file systems
>
> Generally you'll see this error when you're taking a snapshot of a
> journaled filesystem and you haven't applied the VFS-lock patch to the
> kernel. Did you read through the INSTALL file in the 2.1.1 package when
> installing EVMS? Did you follow section 2.B.5?
>
> Also, is this an ext2 or an ext3 filesystem? It will make a difference in
> this case.
>
> > EXT2-fs: device-mapper(254,16)couldn't mount because of unsupported
> > optional features (4).
>
> I don't think I've ever seen this error before. I'll have to search through
> the kernel source to see what triggers it.
>
> > This is a 2.4.21 kernel with device-mapper-1.00.05 and evms-2.1.1. The
> > original volume is an evms volume (EXT2/3), and the snapshot volume is
> > also an evms volume created from a snapshot object (no FS).