Date: Sun, 15 Aug 2010 00:07:40 +0200 From: Roland Smith <rsmith@xs4all.nl> To: stable@freebsd.org Subject: Re: Inconsistent IO performance Message-ID: <20100814220740.GA64697@slackbox.erewhon.net> In-Reply-To: <20100814003631.GA34499@slackbox.erewhon.net> References: <20100813160109.8BDDA1CC3A@ptavv.es.net> <20100813213205.GB29150@slackbox.erewhon.net> <20100813233612.GB4280@lava.net> <20100814003631.GA34499@slackbox.erewhon.net>
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--n8g4imXOkfNTN/H1 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sat, Aug 14, 2010 at 02:36:31AM +0200, Roland Smith wrote: > 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 te= st, > > > 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>; >=20 > Ok, so I tried this; >=20 > dd if=3D/dev/zero of=3D/tmp/foo bs=3D10M count=3D1000 >=20 > 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) >=20 > 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. >=20 > I'll try the same on my laptop topmorrow and see what that gets me. This = desktop > machine is ICH7 with ata(4), laptop is ICH9 with ahci(4). Figures from the laptop running 8.1-RELEASE amd64, ahci driver with the following harddisk; ada0: <ST9320423AS 0002SDM1> ATA-8 SATA 2.x device ada0: 300.000MB/s transfers (SATA 2.x, UDMA6, PIO 8192bytes) ada0: Command Queueing enabled ada0: 305245MB (625142448 512 byte sectors: 16H 63S/T 16383C) Running the same test; dd if=3D/dev/zero of=3D/tmp/foo bs=3D10M count=3D1000 Gives the following results. 10485760000 bytes transferred in 122.625997 secs (85510090 bytes/sec) 10485760000 bytes transferred in 126.081170 secs (83166741 bytes/sec) 10485760000 bytes transferred in 126.101845 secs (83153105 bytes/sec) Which is about 10% faster than on the desktop. 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) --n8g4imXOkfNTN/H1 Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.16 (FreeBSD) iEYEARECAAYFAkxnE6wACgkQEnfvsMMhpyVd4QCfYuUF30TBv3HlIBHqneBs5fj9 eVoAn1lUx+RKVPArnZylOtTreWlcnYEb =4wte -----END PGP SIGNATURE----- --n8g4imXOkfNTN/H1--
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