From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gregory Leblanc Subject: Re: strange performance of raid0 Date: Tue, 17 Feb 2004 09:50:21 -0800 Sender: linux-raid-owner@vger.kernel.org Message-ID: <4032545D.4070105@linuxweasel.com> References: <20040215100432.GA19002@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: <20040215100432.GA19002@rap.rap.dk> To: =?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?= Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Keld J=F8rn Simonsen wrote: > Hi >=20 > I have some strange performance results on a raid0 > I have 4 IDE disks on two controllers, the one on the=20 > motherboard of the duron 1 GHz mackine, the other a promise TX2 plus=20 > SATA + PATA controller. I run kernel 2.4.22 >=20 > The disks and hdparm -t on each of them >=20 > /dev/hdc1 seagate 80 GB 16 MB/s > /dev/sda1 maxtor sata 200 GB 50 MB/s > /dev/sdb7 maxtor 160 GB 54 MB/s Well, if you're lucky, these might be useful as comparative numbers=20 between the different drives on the same system. Just as likely not,=20 though, hdparm rather sucks as a benchmark. > The partitions are al about 5 GB each. >=20 > If I make a raid0 device of all of them I get a thruput of 45 MB/s > IIf I exclude the hdc1 partition, I get around 75 MB/s. > The system is a little loaded - but that would be normal operating > conditions. CPU is 90 % idle. I have about 100 MB free RAM. Let's assume that the above numbers have a basis in reality. :) If=20 you've got disks with widely varying speeds, then the best performance=20 can often be hand from setting up a linear RAID volume, rather than a=20 RAID0. RAID 0 is really designed to have matching disks, as it=20 distributes data evenly across them. With Linear, and ext2 (erm, I'm=20 assuming 3 as well, I haven't heard anything different), you can=20 sometimes get better performance with smaller writes, because ext2=20 "scatters" data around the filesystem, in order to avoid fragmentation.= =20 HTH, Greg - 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