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Subject: Re: IBM blade server abysmal disk write performances
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From: Tim Kientzle <tim@kientzle.com>
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To: Karim Fodil-Lemelin <fodillemlinkarim@gmail.com>
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On Jan 15, 2013, at 6:12 AM, Karim Fodil-Lemelin wrote:

> Hi,
>=20
> I'm struggling getting FreeBSD 9.1 properly work on an IBM blade =
server (HS22). Here is a dd output from Linux CentOS vs FreeBSD 9.1.
>=20
> CentOS:
>=20
> 100000+0 records in
> 100000+0 records out
> 51200000 bytes (51 MB) copied, 1.97883 s, 25.9 MB/s
>=20
>=20
> FreeBSD 9.1:
>=20
> 10000+0 records in
> 10000+0 records out
> 5120000 bytes transferred in 60.024997 secs (85298 bytes/sec)

What exactly was the 'dd' command you used?

In particular, what block size did you specify?

Can you strace the 'dd' command on CentOS to
verify that it's using the actual block size you
specified?

Some programs (I've written at least one) "cheat"
by actually doing larger I/O operations than you
request.  This makes a big difference in performance.

So this could reflect optimizations in GNU dd
more than any difference in the actual disk I/O.

If you want to do a more robust comparison, look
for one of the disk benchmarking programs in ports
and see if it's available (in the same version) for
CentOS.

Tim