From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Robinson Subject: Re: standard performance (write speed 20Mb/s) Date: Sun, 17 Jul 2011 13:51:11 +0100 Message-ID: <4E22DABF.1020807@anonymous.org.uk> References: <201107162140.58883.raid1@fuckaround.org> <4E226464.2030200@hardwarefreak.com> <4E22D167.2010905@anonymous.org.uk> <20110717122230.GB2614@teal.hq.k1024.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20110717122230.GB2614@teal.hq.k1024.org> Sender: linux-raid-owner@vger.kernel.org To: Iustin Pop Cc: Linux RAID List-Id: linux-raid.ids On 17/07/2011 13:22, Iustin Pop wrote: > On Sun, Jul 17, 2011 at 01:11:19PM +0100, John Robinson wrote: [...] >> # dd if=3D/dev/zero of=3Dtest bs=3D4096 count=3D262144 >> 262144+0 records in >> 262144+0 records out >> 1073741824 bytes (1.1 GB) copied, 2.5253 seconds, 425 MB/s >> >> And there's a badblocks running on another drive also on the ICH10. >> >> Having said that, I think mine's wrong too, I don't think my array >> can really manage that much throughput. We should both be using more >> realistic benchmarking tools like bonnie++: > > Or simply pass the correct flags to dd =E2=80=94 like oflag=3Ddirect,= which will > make it do non-buffered writes. That's still not realistic: # dd if=3D/dev/zero of=3Dtest oflag=3Ddirect bs=3D4096 count=3D262144 262144+0 records in 262144+0 records out 1073741824 bytes (1.1 GB) copied, 117.434 seconds, 9.1 MB/s Because this time we're doing a read-modify-write for every 4K block, o= r=20 at least a write for every 4K block. I can fix it up again to work in=20 stripe size amounts: # dd if=3D/dev/zero of=3Dtest oflag=3Ddirect bs=3D1572864 count=3D683 683+0 records in 683+0 records out 1074266112 bytes (1.1 GB) copied, 18.3198 seconds, 58.6 MB/s But it's still not realistic because real I/O does use buffers and=20 doesn't work in magic sizes, so we should be using a more realistic=20 benchmarking tool like bonnie++. Cheers, John. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html