Re: How to boost performance

[aragonx@dcsnow.com]

> On Thu, 17 Jun 2010 09:49:42 -0400
> A more consistent way to test would be to cd into a directory on the
> array,
> and repeatedly run something like:
>
> dd if=/dev/zero of=zerofile bs=1M count=2048 conv=fdatasync,notrunc
>
> ...and implement various tweaks you are trying out between the runs, to
> see
> their effect.
>
> Also, the reason you see the write speed dropping off in the end, is
> because
> your server first fills up its write cache almost at the maximum
> attainable sender's (and network) speed, then, as the space in RAM for
> that
> cache runs out, starts flushing it to disk, reducing the rate at which it
> receives new data from the network. So you see that the 70 MB/sec figure
> is
> totally unrelated to the RAID's performance. The dd test described above,
> thanks to these "conv" flags (see the dd man page) will have much more
> sense
> as a benchmark.

Hi Roman,

While I would agree with you if the performance was the same for reads as
it was writes, that is not the case here.  Additionally, I was not SURE
the where my bottleneck was.  It did not have to be storage related. 
Although I had my suspicions.  That is why I included all the information
I thought was relevant.

That being said, I did try two different DD tests that appear to provide
the same results.  This is a more clean method of testing the storage
subsystem though and will use it for further testing on this issue.

time dd if=/dev/zero of=zerofile bs=1M count=2048 conv=fdatasync,notrunc
2048+0 records in
2048+0 records out
2147483648 bytes (2.1 GB) copied, 28.728 s, 74.8 MB/s

real    0m28.732s
user    0m0.004s
sys     0m23.600s

time dd if=/dev/zero of=zerofile bs=1M count=6144 conv=fdatasync,notrunc
6144+0 records in
6144+0 records out
6442450944 bytes (6.4 GB) copied, 196.618 s, 32.8 MB/s

real    3m16.622s
user    0m0.012s
sys     0m27.726s



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