Date: Sat, 14 Aug 2010 02:36:31 +0200 From: Roland Smith <rsmith@xs4all.nl> To: Clifton Royston <cliftonr@lava.net> Cc: stable@freebsd.org Subject: Re: Inconsistent IO performance Message-ID: <20100814003631.GA34499@slackbox.erewhon.net> In-Reply-To: <20100813233612.GB4280@lava.net> References: <20100813160109.8BDDA1CC3A@ptavv.es.net> <20100813213205.GB29150@slackbox.erewhon.net> <20100813233612.GB4280@lava.net>
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--GvXjxJ+pjyke8COw Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Aug 13, 2010 at 01:36:12PM -1000, Clifton Royston wrote: > > Both figures seem quite low to me? I cannot exactly reproduce your test, > > because I don't have an empty second disk handy, but doing > >=20 > > dd if=3D/dev/zero bs=3D1m count=3D100 of=3D/tmp/foo > =20 > With a total write size of 100MB, aren't you just testing speed of > writing into cache RAM this way? I think you need to write amounts > dramatically greater than the total size of the RAM to get values which > appropriately measure disk speed. <snip> > This also supports that theory - off the top of my head, maximum > theoretical possible write throughput to a similarly sized 7200rpm > drive should be 70MB/s (buffer to disk data transfer rate according to > WDC's specs.) <http://wdc.com/en/library/sata/2879-701277.pdf>; Ok, so I tried this; dd if=3D/dev/zero of=3D/tmp/foo bs=3D10M count=3D1000 10485760000 bytes transferred in 138.304953 secs (75816229 bytes/sec) 10485760000 bytes transferred in 139.125501 secs (75369073 bytes/sec) 10485760000 bytes transferred in 136.149871 secs (77016305 bytes/sec) Which is around 72 MiB/s with filesystem overhead, which sounds about right. The drive was making plenty of noise. The point is that it is _way_ more than the 18-22 MiB/s on a raw disk that Kevin is getting. I'll try the same on my laptop topmorrow and see what that gets me. This de= sktop machine is ICH7 with ata(4), laptop is ICH9 with ahci(4). Roland --=20 R.F.Smith http://www.xs4all.nl/~rsmith/ [plain text _non-HTML_ PGP/GnuPG encrypted/signed email much appreciated] pgp: 1A2B 477F 9970 BA3C 2914 B7CE 1277 EFB0 C321 A725 (KeyID: C321A725) --GvXjxJ+pjyke8COw Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.16 (FreeBSD) iEYEARECAAYFAkxl5Q8ACgkQEnfvsMMhpyUPqQCfZRNSTI7QOlTZcT2tRiX6HLEv WjoAoIzAO725qD+qYyw+7yaR+ztRs7gl =Tks/ -----END PGP SIGNATURE----- --GvXjxJ+pjyke8COw--
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