From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keld =?iso-8859-1?Q?J=F8rn?= Simonsen Subject: Re: strange performance of raid0 Date: Sun, 15 Feb 2004 13:05:25 +0100 Sender: linux-raid-owner@vger.kernel.org Message-ID: <20040215120525.GA19434@rap.rap.dk> References: <20040215100432.GA19002@rap.rap.dk> <1076838850.28006.6.camel@stoneburner.xwredwing.net> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <1076838850.28006.6.camel@stoneburner.xwredwing.net> To: Matt Thrailkill Cc: Keld =?iso-8859-1?Q?J=F8rn?= Simonsen , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Sun, Feb 15, 2004 at 01:54:11AM -0800, Matt Thrailkill wrote: > The you don't get as good performance because hdc1 is slow enough to > really drag it down. Think about it, if reads are all going about > sequentially, it has to spend alot of time waiting on that 16mb/s dri= ve > compared to the others. I would have thought the disks would have worked towards gaining performance enhancements in some cumulative way, is that not so, in the= ory? So why is 3 disks slower than 2? > You probably can't get 100mb/s with the two because that would be pre= tty > efficient, and there's probably more overhead than that. >=20 > Shouldn't the 80gb drive be going faster than 16mb/s though? Have yo= u > checked hdparm to make sure dma and all the goodies are turned on for > it? I have a 40 GB segate disk also, on the same motherboard IDE controller, it runs about 40 MB/s. So yes, the hdc1 should go faster, and I have measured something like 40 MB/s on it in idler times. I think it is because it is running other=20 processes. The machine is a ftp mirror and the disk has RedHat and Fedora ISO images, so it is quite popular. > On Sun, 2004-02-15 at 02:04, 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 plu= s=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 > >=20 > > 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. > >=20 > > Why is it slower with 3 disks in the raid0 than > > 2 disks? Why don't I get approx 100 MB/s out of just the two? > >=20 > > Best regards > > Keld - 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