[lustre-discuss] Lustre [2.8.0] flock Functionality

Martin Hecht hecht at hlrs.de
Wed Mar 29 06:54:43 PDT 2017


we use the flock mount option on all our lustre systems (currently some
2.5 versions) and are not aware of any issues due to that.

If your applications run on a single node (or require  locks only
locally) you could also try localflock.
localflock has less performance impact than the global flock. How much
impact you have depends on how heavily the applications make use of
locks. We have measured a few per cent on lustre 1.8 in simple tests,
but I think that the performance impact nowadays is even less, but as I
said, it depends on the IO pattern.

localflock is more risky than flock, because it makes your application
think that locks are there, but in fact they are not globally visible,
which may lead to strange effects with parallel applications spanning
several nodes. We were running localflock on one of our systems for some
time and occasionally heard about such problems from a few users.

best regards, Martin

On 03/28/2017 07:49 PM, DeWitt, Chad wrote:
> Good afternoon, All.
> We've encountered several programs that require flock, so we are now
> investigating enabling flock functionality.  However, the Lustre manual
> includes a passage in regards to flocks which gives us pause:
> "Warning
> This mode affects the performance of the file being flocked and may affect
> stability, depending on the Lustre version used.  Consider using a newer
> Lustre version which is more stable. If the consistent mode is enabled and
> no applications are using flock, then it has no effect."
> We are running Lustre 2.8.0 (servers and clients).  I've looked through
> Jira, but didn't see anything that looked like a showstopper.
> Just curious if anyone has enabled flocks and encountered issues?  Anything
> in particular to look out for?
> Thank you in advance,
> Chad
> ------------------------------------------------------------
> Chad DeWitt, CISSP | HPC Storage Administrator
> UNC Charlotte *| *ITS – University Research Computing
> ------------------------------------------------------------

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