[Lustre-discuss] Multiple MDTs with Lustre 1.6?

[Kilian CAVALOTTI]

Hi Klaus,

On Friday 12 October 2007 10:18:49 am Klaus Steden wrote:
> I have redundant MDS/MDT servers, and when generating their
> /etc/fstab files, I have them both list the MDT volume under their
> mounted drives (so that they both mount the metadata volume). Being a
> bit of a neophyte, I¹m not sure if this is the right thing to do. Is
> this going to cause a problem in future? What are the possible
> consequences of both hosts mounting the same metadata volume
> simultaneously? How do the OSTs handle this situation?

I'm afraid mounting the MDT device on both hosts is a very bad idea. Not 
only for Lustre, but in a general fashion, unless you're using some 
specific filesystem which has been designed in that goal (like OCFS2 or 
GFS). A 'standard' filesystem like ext3 can't handle simultaneous 
writes from different hosts at the same time. It's likely to cause 
heavy data corruption in the MDT filesystem, and the OSTs are not 
supposed to deal with anything like that.

You can still reference the MDT device in both MDS' fstab, but be sure 
you add the "noauto" option so the volume won't be mounted at boot. It 
will be the high-availability provider's job (likely heartbeat) to deal 
with mounting the MDT device on the active MDS.

See 
http://manual.lustre.org/manual/LustreManual16_HTML/DynamicHTML-08-1.html#wp1035482 
for more details.

Cheers,
-- 
Kilian