[PVFS2-users] slow read and write

[Alan Louis Scheinine]

Neill asked me: Can you report back some read results using the pvfs2-cp 
utility?  Are they similar?

Yes, but that is not the same thing.  Here is the result

pvfs2-cp -t /pvfs2/bigtestfile1 /scratch/delete_me
Wrote 500000000 bytes in 4.911304 seconds. 97.089726 MB/seconds

where the disk /scratch is local.  The problem with "cp" is
that the speed is limited by the local disk that is the
destination.
Using the local disk and my watch I find
cd /scratch
  cp bigtestfile3 deleteme2   about 9.5 seconds
  cp bigtestfile3 deleteme3   about 3.7 seconds
where bigtestfile3 is not on /pvfs2 but is identical to
the file on /pvfs2.  The first line is the first copy of
the file today and the second line repeats the copy.
The client machine has only one hard disk so the first line
represents read and write whereas the second line represents
writing from memory cache.  The time for pvfs2-cp for a file
of the same size is 4.9 seconds (as we see above).  So the
writing to local disk is not necessarily the bottleneck but
one cannot expect much better using the pvfs2-cp command
when reading from /pvfs2 (distributed on 8 servers).  To see
if the distributed servers can do an order of magnitude better
it is necessary to use a program that reads without writing.
Since 8 servers connected with gigabit ethernet have their
ethernet packets concentrated to a client with a 10 gigabit
ethernet connection using a good-quality switch (Extreme),
the kind of test I would like to do is to achieve an order
of magnitude better performance.



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