Re: Inconsistent IO performance
--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--
討論串 (同標題文章)
完整討論串 (本文為第 7 之 24 篇)：