On Thursday, October 21, 2010 02:07:39 pm you wrote:
> Hello,
> I have a requirement to share (read/write) a set of files (XML) between two
> zLinux guests under the same zVM LPAR.
> The zLinux guests will run WebSphere and update the same set of files.
> Can I define an mdisk as "MWV" and allow the zLinux guests to share?
> Or would it be prudent to setup something like NFS to handle the sharing?
> I'm not sure of the frequency of updates, but I don't think it would be
> very heavy.
Don't define the MDISKs to both be writable filesystems on each guest, because
that risks corrupting the filesystems. Use NFS instead.
If you search the list archives you'll find discussions on this, but here's
the short explanation of why sharing read-write MDISKs between Linux guests is
dangerous. If you mount the same filesystem read-write on two Linux guests,
both will be caching blocks from that filesystem. If one guest changes a
block, the other may not see the change because it reads from its cache
instead of the disk. If the second one then changes that block, they are
overwriting the change made by the first guest. If that block happens to
contain a directory, or part of the filesystem's hash table, you've just
trashed things badly.
So use NFS, because there's only one Linux guest caching that filesystem.
- MacK.
-----
Edmund R. MacKenty
Software Architect
Rocket Software
275 Grove Street - Newton, MA 02466-2272 - USA
Tel: +1.617.614.4321
Email: [email protected]
Web: www.rocketsoftware.com
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