[Lustre-discuss] OST redundancy between nodes?

[Kevin Van Maren]

Gary Gogick wrote:
> Heya all,
>
> I'm investigating potential solutions for a storage deployment.  
> Lustre piqued my interest due to ease of scalability and awesome 
> aggregate throughput potential. 
>
> Wondering if there's any provision in Lustre for handling catastrophic 
> loss of a node containing an OST; eg. replication/mirroring of OSTs to 
> other nodes?
>
> I'm gathering from the 1.8.0 documentation that there's no protection 
> of this sort for data other than underlying RAID configs on any 
> individual node, at least not without attempting to do some 
> interesting stuff with DRDB.  Just started looking at Lustre over the 
> past day though, so I'd totally appreciate an authoritative answer in 
> case I'm misinterpreting the documentation. :)

Correct.

Lustre failover can be used to support catastrophic failure of a _node_, 
but not the _storage_.  If your configuration makes LUNs available to 
two nodes, it is possible to configure Lustre to operate across the 
failure of a server.

If your LUN fails catastrophically, all the data on that lun is gone.  
It is possible to bring Lustre up without it, but none of the files on 
that OST would be available.  If you are concerned about this case, then 
backups are your friend.

While drdb could be used to make a lun "available" to two nodes, it will 
have a significant impact on performance, and (AFAIK) does not do 
synchronous replication, so an fsck would be required prior to mounting 
the OST on the second node, and there would be some data loss.

Kevin