[Lustre-discuss] Lustre directory sizes - fast "du"

[Andreas Dilger]

On Sep 04, 2008  18:55 +0100, Peter Grandi wrote:
> > Hi all, since our users have managed to write several TBs to
> > Lustre by now, they sometimes would like to know what and how
> > much there is in their directories. Is there any smarter way
> > to find out than to do a "du -hs <dirname>" and wait for 30min
> > for the 12TB-answer ?

One possibility would be to enable quotas with large limits for every
user that won't hamper usage.  This will track space usage for each
user.

Depending on your coding skills it might even be possible to change
the quota code so that it only tracked space usage but didn't enforce
usage limits.  This would potentially reduce the overhead of quotas
because there is no need for OSTs to check the quota limits during IO.

> If you have any patches that speed up the fetching of (what are
> likely to be) millions of records from random places on a disk
> very quickly, and also speed up the latency of the associated
> network roundtrips please let us know :-).

That is always our goal as well :-).

> I've already told them to substitute "ls -l" by "find -type f
> -exec ls -l {};", although I'm not too sure about that either.

I don't think that will help at all. "ls" is a crazy bunch of
code that does "stat" on the directory and all kinds of extra
work.  Possibly better would be:

lfs find ${dir} -type f | xargs stat -c %b

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