From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Robinson Subject: Re: Awful RAID5 random read performance Date: Wed, 03 Jun 2009 00:13:05 +0100 Message-ID: <4A25B201.2000705@anonymous.org.uk> References: <20090531154159405.TTOI3923@cdptpa-omta04.mail.rr.com> <200905311056.30521.tfjellstrom@shaw.ca> <4A25754F.5030107@tmr.com> <20090602194704.GA30639@rap.rap.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20090602194704.GA30639@rap.rap.dk> Sender: linux-raid-owner@vger.kernel.org To: =?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?= Cc: Linux RAID List-Id: linux-raid.ids On 02/06/2009 20:47, Keld J=F8rn Simonsen wrote: [...] > My perception is that raid10,f2 is probably the fastest also for smal= l random > reads because of the lower latency, and faster transfer times due to = only > using the outer disk sectors. For writes the elevator evens out the > ramdom access. Benchmarks may not show this effect as they are often > done on clean file systems, where the files are allocated in the > beginning of the fs. >=20 > For cases where you need cheap disk space, and have big files like > .iso's then raid5 could be a good choice because it has the most spac= e > while maintaining fair to good performance for big files.=20 >=20 > In your case, using 3 disks, raid5 should give about 210 % of the nom= inal > single disk speed for big file reads, and maybe 180 % for big file > writes. raid10,f2 should give about 290 % for big file reads and 140% > for big file writes. Random reads should be about the same for raid5 = and > raid10,f2 - raid10,f2 maybe 15 % faster, while random writes should b= e > mediocre for raid5, and good for raid10,f2. I'd be interested in reading about where you got these figures from=20 and/or the rationale behind them; I'd have guessed differently... 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