[Lustre-discuss] Regarding redundancy

[Arne Wiebalck]

Brian,

> Unless you also lose clients, no.  In the event of an OSS going down,
> the client will not have gotten the reply back from the OST to say that
> it's data was actually written to disk.  Until the client gets such a
> reply, it holds on to that data so that if an OSS does crash, it can
> "replay" that transaction.  Thus, all data is either physically on-disk,
> on in client memory ready to be replayed to disk.

what about if you have multiple clients, all having transactions with
the OSS open. Now the OSS goes down and comes back. From what I
understand, the server goes into recovery and rejects new connections 
before recovery is finished (correct?). What if all but one client
reconnect, i.e. you lose one client: are the transactions of the
successfully reconnected clients replayed or are they discarded?

> > I
> > also would like to know if you can dynamically add to the cluster new
> > OSS/OST's or do you have to unmount the client then remount after
> > doing so.
> 
> No.  You just add them as you need.
> 

Independent from the load? I think the 'official' statement was that the
cluster has to be quiescent, i.e. no client activity. Is that (still)
true?

TIA,
 Arne