From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roman Mamedov Subject: Re: mdadm raid1 read performance Date: Thu, 5 May 2011 10:06:10 +0600 Message-ID: <20110505100610.66c93e08@natsu> References: <20110504105822.21e23bc3@notabene.brown> <4DC0F2B6.9050708@fnarfbargle.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/5B9roHYFR3afGm34sicdbWU"; protocol="application/pgp-signature" Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Liam Kurmos Cc: Roberto Spadim , Brad Campbell , Drew , NeilBrown , linux-raid@vger.kernel.org List-Id: linux-raid.ids --Sig_/5B9roHYFR3afGm34sicdbWU Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Thu, 5 May 2011 00:08:59 +0100 Liam Kurmos wrote: > in my tests i read 1GB and throw away the data. > dd if=3D/dev/md0 of=3D/dev/null bs=3D1M count=3D1000 If you have enough RAM for disk cache, on the second and further consecutive invocations of this you will be reading mostly from the cache, giving you an incorrect inflated result. So either don't forget to drop filesystem caches between runs, or just test read performance with "hdparm -t /dev/mdX" inste= ad. --=20 With respect, Roman --Sig_/5B9roHYFR3afGm34sicdbWU Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iEYEARECAAYFAk3CIjIACgkQTLKSvz+PZwhdUgCfYPCuxKoX3SLCNxXvmg89yKxQ 0DsAniCCV3nmOCH1PhDEgXBrdHbsy4MP =ZLTn -----END PGP SIGNATURE----- --Sig_/5B9roHYFR3afGm34sicdbWU--