Hi, 
This is possible in version 1.6 (and in the betas).  Just format and
mount the OST, it will be added to the cluster.
See: https://wiki.lustre.org/lustre/MountConf
Good luck.
- Peter - 
 > -----Original Message-----
 > From: lustre-discuss-bounces@clusterfs.com 
 > [mailto:lustre-discuss-bounces@clusterfs.com] On Behalf Of 
 > Brian Taber
 > Sent: Wednesday, August 23, 2006 11:00 PM
 > To: lustre-discuss@clusterfs.com
 > Subject: [Lustre-discuss] Adding OST wile running
 > 
 > Is it possible to add an OST while the MDS is running and be 
 > available without restarting the MDS?  If so, how?
 > 
 > -------------------------
 > Brian Taber
 > Owner/IT Specialist
 > Diverse Computer Group
 > Office: 774-206-5592
 > Cell: 508-496-9221
 > btaber@diversecg.com
 > 
 > 
 > 
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 >