[Pvfs2-users] metadata tests using mdtest

[Phil Carns]

>>> I am trying to use LLNL's mdtest
>>> [http://sourceforge.net/projects/mdtest/] on pvfs2.
>>>
>>> It works by passing an argument to the test indicating which directory
>>> the test must run. However when I do indicate the directory as
>>> /mnt/pvfs2 - the test runs on the local directory and doesn't use PVFS2.
>>> If I do add the prefix , as "pvfs2:/mnt/pvfs2" , the test reports back
>>> that it cannot find the filesystem. Although my mpich libraries are
>>> linked with the pvfs2 libraries.
>>>
>>> Any ideas about this?
>>>     
>> Yep, LLNL''s mdtest uses MPI for coordination but POSIX for metadata,
>> so the 'pvfs2:' prefix won't work for that test (it works for the
>> mpi-md-test in the PVFS CVS).
>>
>> What version of mdtest are you using? You are giving mdtest the '-d'
>> option?  I can't think of a reason for mdtest to ignore your testdir
>> option and start doing stuff in the local directory...
>>   
> I apologize for the delay in replying.
> 
> I use version 1.7.4 - which seems to be the latest build on their
> sourceforge page.
> 
> The mdtest does not ignore my prefix option. Here's what happens. AFAIK,
> while using PVFS2 on a cluster there is no requirement to perform a
> mount operation. As I understand since the MPICH binaries are linked to
> the PVFS2 libraries, the MPI app/bechmark would understand how to locate
> the PVFS2 storage servers [apart from the /etc/pvfs2tab content] .
> Hence there exists a directory /mnt/pvfs2 on each of my compute nodes.

Hi Nirmal,

Your assumption is only true if the MPI app/benchmark uses functions 
like MPI_File_open(), MPI_File_write(), etc. to access the file system. 
  Those functions are part of the MPI-IO interface.  mdtest does not do 
this.  In mdtest.c it is just doing normal open() and write() calls. 
You therefore won't be able to use mdtest to test PVFS unless you mount 
the PVFS file system.  As you are running it right now it is probably 
just creating files in your local file system under /mnt/pvfs2, which is 
why they don't show up in pvfs2-ls.

-Phil