[lustre-discuss] Mounting lustre with some OST missing

Tung-Han Hsieh thhsieh at twcp1.phys.ntu.edu.tw
Thu Dec 13 02:24:02 PST 2018

Dear All,

I am asking whether it is possible to mount lustre when some of the
OSTs are missing.

The situation is following. We have some old systems running Lustre
version 1.8.8. One of the file server which contains several OSTs
were broken, and need some time to repair. In the meantime, we are
urgent to copy some data out of the lustre file system in order
to continue our works. But without the OSTs of that broken file
server, presumably we cannot mount the lustre file system.

Is there a trick to temporarily mount the lustre file system even
read only ? I know that we can remove the OSTs in the broken file
server by running these command in the MDT server:

lctl conf_param foo-OSTXXXX.osc.active=0

Then we are able to mount it. But when the file server is repaired,
could we safely add its OSTs back to the lustre file system and
recover all the data in these OSTs ?

If the answer to the previous question is "yes", then what will
happen if, before the broken file server coming back, the MDT server
accidently needs reboot ? In this case can we still add back these
OSTs safely when that file server is repaired ?

Or, is there a better way to temporarily mount it in read only ?

Thank you very much for your help.


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