[Darshan-users] Unexpected Darshan I/O characterization running IOR BM

Carns, Philip H. carns at mcs.anl.gov
Wed Nov 21 14:46:21 CST 2018

Hi Cormac,

That's strange.  The -i 2 and -m options are making IOR attempt to read two files: testfile.0 and testfile.1.  Darshan is definitely aware of those files, but not only are the read counters missing but also the open counters.  It only shows a stat from each rank for the files in question.

Can you confirm that both of the files exist and are big enough to accommodate the requested read volume?  I wonder if IOR might stat the files up front and exit early if they aren't the correct size?

Could you also share the output of "ldd ior"?  I'm curious to make sure there isn't anything unusual about the libraries linked in, but usually if that were a problem you wouldn't get a log at all.

Also one last idea, does the behavior change if you remove the -B (O_DIRECT) option?  That shouldn't matter from Darshan's perspective, but it might not hurt to check.


On 2018-11-20 19:59:55-05:00 Darshan-users wrote:

I recently installed Darshan 3.1.6 on Microsoft Azure VM running Centos 7.4.
I got an unexpected result using Darshan to characterize the I/O for an IOR benchmark
export LD_PRELOAD=/avere/apps/spack/linux-centos7-x86_64/gcc-4.8.5/darshan-runtime-3.1.6-daohky4yevagxajjl33lwk472lcgn6g4/lib/libdarshan.so
mpirun -np 8 ior -a POSIX -B -r -k -z -v -o $FILEPATH -i 2 -m -t 32m -b 256M -d 1
After the job completed, a Darshan log file was created, the resulting text report (darshan-parser_ior_read_shared.out, its attached) was generated using the following command
darshan-parser  --all testuser_ior_id22-20-80229-14589323501426222819_1.darshan >& darshan-parser_ior_read_shared.out
The above IOR benchmark is a read only benchmark to a shared file system, but the resulting darshan report indicates there are no READ operations?
Any ideas why the resulting Darshan resport has no read operations? (Note if I add a -w option to the above IOR benchmark  (i.e do a write and read to a shared filesystem, darshan only
reports the writes and not reads?)
Any help would be appreciated,
Thanks for your support,
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