[Lustre-discuss] remote volume mirroring

[Andreas Dilger]

On Jun 29, 2009  20:31 -0500, Brian O'Connor wrote:
> I'm not hopefull, but I notice that some raid devices support
> remote volume mirroring. 
> 
> ie.
> 
> http://www.lsi.com/DistributionSystem/AssetDocument/documentation/storag
> e/software/ESG_RVM_PB_030608.pdf
> 
> if the MDS/MGS and OSS's are on a raid devices that support
> RVM, could I use this to sync a production and remote DR lustre
> cluster?

Yes, so long as the remote mirroring is done in an ordered manner (i.e.
it doesn't reorder blocks and cause filesystem inconsistency).  If the
mirror is not synchronous then the clients won't be able to recover
transparently in all cases, because the mirror filesystem may have lost
some state that the clients were told was committed to stable storage.

In all but the most unusual cases, however, even with an unordered sync
between devices you would be able to mount the filesystem after a full
e2fsck run.  It would be better to have the mirror be ordered, however.

> I seem to remember that even if this works I'll only be able to mount
> the lustre volumes on the remote site if I use the same IP numbers in
> everything. Are there any other hardware dependancies that would
> stop an active block level lustre mirror.?

Not AFAIK.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.