From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nikolay Kichukov Subject: Re: mdadm raid1 read performance Date: Thu, 05 May 2011 11:06:09 +0300 Message-ID: <4DC25A71.6090705@oldum.net> References: <20110504105822.21e23bc3@notabene.brown> <4DC0F2B6.9050708@fnarfbargle.com> <20110505100610.66c93e08@natsu> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20110505100610.66c93e08@natsu> Sender: linux-raid-owner@vger.kernel.org To: Roman Mamedov Cc: Liam Kurmos , Roberto Spadim , Brad Campbell , Drew , NeilBrown , linux-raid@vger.kernel.org List-Id: linux-raid.ids -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi, It seems like he is reading directly from the raid device and not through the filesystem. So there are no filesystem caches in this way. Cheers, - -Nik On 05/05/2011 07:06 AM, Roman Mamedov wrote: > 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=/dev/md0 of=/dev/null bs=1M count=1000 > > 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" instead. > -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iQEcBAEBAgAGBQJNwlpxAAoJEDFLYVOGGjgXHS0IAJAVFwR0Y0SD6G4CTaViqNCv 32s/VCZWTZMzXiLOrY5xCGFiuqPurmGLy/+aW+HeEYShMndkZQ8H8ZHlSx5L3OoH SQnWS7gP5hUn2w9qamhtFk9iPWpx18ZzVqN/k9WyAWhY4Ro20G8PWI3/T4Q3+zam WYJ6KglllX+BuQYVhmhwB1KGVFhmpQXBXKWVrcGIB7vyGnM5K9fWLbxd6VvghZvd qpfrmPO2WvuqpxCS+YcZTqEg7osbzNB+W/6DMJ7BpxyUcxIEyXwBwZSUxsZe3WWo oTfj0XUaVc17TPfKMCyLfgm+K6f+IJfKky5e5mJyFCjesDhqFngkpilft9xNxq0= =qsmJ -----END PGP SIGNATURE-----