Dear Osama,
thanks for pointing this out.
I was not aware of this problem.

I now made some modifications to mdtest to compensate for this limitation.
Now it can limit the number of files per directories creating one
extra top-level directory if needed.
E.g. with a limit of 50 files and a total of 200 files, one would see
in the top-level testing directory:
#test-dir.0-0
#test-dir.0-1
#test-dir.0-2
#test-dir.0-3

The subdirectory tree of each directory is the complete tree as before
under #test-dir.0-0.
There is no synchronization when switching between these trees.
I expect that this emulates very well the behavior of a single large
directory but well there is no perfect solution.


The stuff is already integrated into the testing branch of io-500-dev.
To use it:

In io-500-dev
$ git checkout testing
$ ./utilities/prepare.sh

in io500.sh
Line 85:
io500_mdtest_hard_other_options=""
Change that to:
io500_mdtest_hard_other_options="-I 8000000"
Which effectively will create a directory for each batch of 8M files.
Note that the number of items (-n) must be a multiple of (-I)

Note that that feature cannot be used with stonewalling at the moment!
At some point, the mdtest code needs a redesign to allow such changes.

Hence, set in L30:
io500_stonewall_timer=0

If you want to give it a try, I would welcome it...

Best,
Julian

2018-07-26 3:05 GMT+01:00 Osamu Tatebe <tatebe@cs.tsukuba.ac.jp>:
> Hi,
>
> I would like to remind an issue regarding mdtest-hard benchmark.  It
> creates files in a single directory for at least five minutes.  When
> the metadata performance is more improved, the greater number of files
> will be created.  This will hit the limit of the number of files in a
> single directory.
>
> Actually, the limit of Lustre file system is about 8M files although
> it depends the length of the pathname.  When the metadata performance
> is better than 27K IOPS, it is not possible to execute the mdtest-hard
> create benchmark for five minutes since the number of files is larger
> than 8M.
>
> This is a reason we cannot submit the Lustre result.  I expect this
> will be quite common when the metadata performance is more improved.
>
> Regards,
> Osamu
>
> ---
> Osamu Tatebe, Ph.D.
> Center for Computational Sciences, University of Tsukuba
> 1-1-1 Tennodai, Tsukuba, Ibaraki 3058577 Japan
> _______________________________________________
> IO-500 mailing list
> IO-500@vi4io.org
> https://www.vi4io.org/mailman/listinfo/io-500



--
Dr. Julian Kunkel
Lecturer, Department of Computer Science
+44 (0) 118 378 8218
http://www.cs.reading.ac.uk/
https://hps.vi4io.org/
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