Rob Ross wrote:
Hi Henk,
Please be sure to CC pvfs2-users on future emails.
Sorry stupid I didin't do that.
Without any additional information, my guess is that every application
you're using in this workflow performs very small I/Os. These operations
are passed into the kernel, back out to pvfs2-client, across the network
and received by the PVFS server, who then performs I/O on your
application's behalf. If operations are particularly small, this can be
a lot of overhead.
Top tells me that server-side 99.6% idle client-side 95% idle, how could
I determine what is causing the abnormal delays.
Starting to play a dvd takes about 12 secs. After a few seconds it
starts stuttering.
By nfs of 1 of the servers it takes about 1 sec to start and never stutters.
Other networked file systems can hide some of this latency by caching
data (either coherently or not) on the client. PVFS does not do this, so
each little operation goes across the wire.
Can this be investigated with some networktool and if yes, how ?
There's really no advantage
to using a parallel file system for the workload you have described,
But should the disadvantage be in this order of magnitude ?
unless you're planning on having a lot of systems doing this process in
parallel and want a single place to store the output.
What sort of network do you have in this system? What sort of nodes are
you using for the PVFS servers?
All AMD 4000+ systems with 1Gb networkcards and 320GB disk in each or them.
Copying from to clients to these 3 servers is > 100MB/sec pretty close
to what Gb ethernet can do.
Regards
Henk Schoneveld
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