[MPICH] MPI IO write permissions and locks, acceptable bandwiths in your experiments

[Luiz Mendes]

Hi all,

Well, i got a program that make a kind of benchmark that measure the
transfer rate of process writes into a file, in my case i am working with
shared folder provided by NFS Server between two machines.

I would like to know your experiences with MPI IO over NFS and other file
systems. What ranges of transfer rates did you get in your tests.

With a certain program here that generates random numbers and writes them
into a file in shared folder, i got with one local process, transfer rates
about 350 MB/s, with 2 local processes 570 MB/s.

Well i see some articles about I/O tests, and the high transfers rate are
about 700 MB/s. Then i think if this rates that i got here are correct. Do
you recomend some benchmark to test I/O operations?

When i try to use 2 processes, being one of them non local, i got out of
range values for transfer rate and no writes for no one of them . Then i
tried to execute this program in the slave node usign ssh, then i access the
non local node by ssh, and execute there the program. For my surprise, in
this case, it writes for the 2 processes, however during the execution a
"**io permission denied" messages have appeared, the writes have executed on
the 2 processes, local and no local, and offsets correclty figure out. The
transfer rate now, decreased a lot, only 10MB/s.

Do you know something that could be causing this problems?

Thaks for all for the previous helps, thanks Geoff J.

Sorry for my poor english.
Luiz Mendes
UFJF
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