[Lustre-discuss] OST went down running Lustre 1.6.6

Brian J. Murrell Brian.Murrell at Sun.COM
Wed Feb 11 08:00:04 PST 2009


On Wed, 2009-02-11 at 10:46 -0500, Brian Stone wrote:
> Yes, I was using corruption to mean incomplete files.

Ahhh.  OK.  That can be an artifact of a failure to complete recovery.

> So, let me 
> rephrase, is there a way to avoid "incomplete files" after an OSS crash, 

Yes, make sure that all clients are available to reconnect and
participate in recovery.

> The lustre devices were not deactivated from the clients 
> and MDS, would that possibly avoid the purge of data?

No.  You are free to reboot an OSS any time you wish.  All clients will
wait for it to come back up and recovery will proceed and complete, if
all clients are still present to participate.

Recovery is basically a process by which clients have an opportunity to
retry any recent (i.e. in progress) transactions that may have gotten
"lost" while an OSS crashes or reboots.  Until the OSS confirms to the
client that it has written a given transaction to stable storage,
clients hold on to them in case it needs to replay them.

In the event of a crash, all clients reconnect and offer their recent
transactions, however this must (currently) be done, serially, in the
same order they were done originally.  If a given client fails to
connect, the server cannot know that it did not have any transactions to
commit and must therefore discard all further transactions and abort
recovery, which can lead to this "data loss".

b.

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