[Beowulf] NFS over RDMA performance confusion

holway at th.physik.uni-frankfurt.de holway at th.physik.uni-frankfurt.de
Thu Sep 13 08:21:21 PDT 2012


> I assume so, but just to be clear you witnessed this behavior even with
> the -I (directio) parameter?

Yes.

for i in 1 2 4 8 16; do /cm/shared/apps/iozone/current/sbin/iozone -I -l
$i -u $i -r 16k -s 10M -F file1..file16 ; done > output &

>
>>> Can anyone tell me what might be the bottleneck on the single machines?
>>> Why can I not get 180,000 IOPS when running on a single machine.
>
> Can you rerun those tests with, 16 and 32 procs?  I've run into some
> pretty wacky relationships between numbers of cores, procs, and disks in
> the subsystem.  I assume your machine has 8 cores, and I tend to find
> around 2 processes per core to be ideal if the number of disks your
> trying to run against are greater than the number of cores.  This is a
> really handwaving rule-of-thumb, but it's served me alright in the past
> as a first benchmark.

1 proc	Children see throughput for 1 random writers 	=   46036.32 KB/sec
2 proc	Children see throughput for 2 random writers 	=   82828.13 KB/sec
4 proc	Children see throughput for 4 random writers 	=  126709.65 KB/sec
8 proc	Children see throughput for 8 random writers 	=  190070.96 KB/sec
16 proc	Children see throughput for 16 random writers 	=  273970.94 KB/sec

1 proc	Children see throughput for 1 random readers 	=  109169.52 KB/sec
2 proc	Children see throughput for 2 random readers 	=  202556.82 KB/sec
4 proc	Children see throughput for 4 random readers 	=  381504.25 KB/sec
8 proc	Children see throughput for 8 random readers 	=  719108.27 KB/sec
16 proc	Children see throughput for 16 random readers 	= 1152648.13 KB/sec

Just to be clear, I do not want to test the performance of ZFS. Just NFS
at the moment.

Before I got the ZFS box I was exporting a tmpfs over the NFS.

I am quite sure I am not doing any local caching.

Why is each process IO limited like that?

Thanks,

Andrew

>
> Best,
>
> ellis
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