I've been using this scenario for database backups since we had the
discussion about shared VM disks on this thread about a year ago.
David made the point then that if you had a hipervisor that allowed it,
not making a disk dependent on one of the machines being up at all times
(as with NFS), had some advantages.. I also used Tore's suggestion to
stick to ext2 so nobody would try to replay a journal. .I use them
for database backups that I take each night, and for SLES10 (both SP1
and SP3) it works fine. IF the RW linux is down (usually because it
didn't come up again), caching won't be an issue.
If the machine that 'owns' the database/disk is down, I can still see
the database, and can recover a copy on the machine that has RO access.
without having to go in and change the VM configuration. It's also easy
to
check to see that the backup went ok. and the recovery would work.
I haven't tried sharing a disk between 2 SLES 11 machines yet, and
that's where I'm going with upgrades. If it doesn't work, it would be
nice to know. Why would the fact that one of the machines has the disk
mounted RW
keep the other(s) from seeing it at all?
Best Regards/
Med vennlig hilsen
Roger Evans
________________________________________________________________________
On Tue, 2011-10-11 at 10:11 -0600, Mark Post wrote:
> >>> On 10/11/2011 at 04:26 AM, Roger Evans <ro...@autodata.no> wrote:
> > I am trying to mount a disk R/O from two linux machines on one VM. One
> > of them is SLES10 where the disk is defined in zipl.conf. The other
> > is a new SLES11 ('CLPRODB2)..
> >
> > The disk is mounted RW on a SLES10sp3 machine.
>
> This is never a good idea. If you want to share a disk between z/VM guests,
> _all_ of them need to have it read only. None of them can have it
> read-write. There's too many layers of caching going on for it to work
> reliably, if at all.
>
> If you absolutely have to have access to a disk that is mounted read-write,
> use NFS to export it read only.
>
>
> Mark Post
>
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