Hi, A follow-up to my own post. I did not look well enough. The MGS "lctl dl" showed one device indeed missing even though I did not deactivate it and it is on the OSS correctly. The error message about "OST index 0 missing" is that on the MGS crew2-OST0000 is missing. [root at mds1 ~]# lctl dl 0 UP mgs MGS MGS 5 1 UP mgc MGC192.168.64.210 at o2ib ab3c594f-d965-b3c2-9180-121ffcf236cd 5 2 UP mdt MDS MDS_uuid 3 3 UP lov crew2-mdtlov crew2-mdtlov_UUID 4 4 UP mds crew2-MDT0000 crew2mds_UUID 4 5 UP osc crew2-OST0001-osc crew2-mdtlov_UUID 5 6 UP osc crew2-OST0002-osc crew2-mdtlov_UUID 5 There should be a "crew2-OST0000". On the OSS, I have issued a "mount -o remount /srv/lustre/OST/crew2-OST0000". The disk is seen on the OSS in a "df". Again, no errors on the OSS nor the MGS. I have also tried to remount the MGS crew2 MDT disk. No change. What I need is something like an "lctl activate crew2-OST0000". That command uses the NID and in this instance I have no NID to activate. The unmounting/mounting of the MDT did not cause a re-read of the OSS disks. Is there a way in which I can add the OST back in? It should not have been omitted in the first place. Cheers! megan