[Lustre-discuss] Lustre attribute caching?

[Andreas Dilger]

On May 18, 2009  12:16 +0200, Daniel Kobras wrote:
> On Mon, Apr 27, 2009 at 01:29:20AM -0600, Andreas Dilger wrote:
> > Lustre will cache negative dentries as long as the directory is not
> > modified.  If the directory has a new file created or an existing
> > one deleted then the negative dentries, along with the rest of the
> > readdir data is removed from all client caches, though the individual
> > inodes can still live in the client cache as they have their own locks.
> 
> Interesting. Thanks for the info! This makes me wonder how Lustre copes
> with temporary network outages in this case. If the client drops off the
> net, the server cannot invalidate the caches. Does the client notice the
> communication problem, or could it briefly serve stale data?

Lustre is cache coherent even after network failures.  If the client had
any lock that changed state while it could not communicate with the server,
the server will evict the client, which forces the client to discard all
of its saved state when it reconnects.  If no client locks changed while
it was disconnected then the client just reconnects and continues on its way.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.