From mboxrd@z Thu Jan 1 00:00:00 1970 From: "J. Ryan Earl" Subject: RE: RAID1 & 2.6.9 performance problem Date: Tue, 18 Jan 2005 11:32:54 -0600 Message-ID: References: <41EBD827.80701@pipi.ma.cx> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-2" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <41EBD827.80701@pipi.ma.cx> Sender: linux-raid-owner@vger.kernel.org To: Janusz Zamecki , linux-raid@vger.kernel.org List-Id: linux-raid.ids "Please check this out: hdparm -t /dev/hdg /dev/hde /dev/md6 /dev/hdg: Timing buffered disk reads: 184 MB in 3.03 seconds = 60.76 MB/sec /dev/hde: Timing buffered disk reads: 184 MB in 3.01 seconds = 61.08 MB/sec /dev/md6: Timing buffered disk reads: 184 MB in 3.03 seconds = 60.74 MB/sec I've expected much better /dev/md6 performance (at least 100MB/s)." This is perfectly normally, I'm not sure why you'd expect better performance. You will get 2 parallel sequential reads at around 120MB/sec assuming you're not bus limited. A single sequential parallel read can be no faster than the performance of a single RAID1 disk, though latency should lower significantly. I found that average number of read seeks/sec increases around 80% in going from a single HD to a RAID1 setup. Think about it and it should make sense. You have two discs with identical layouts. How could you possibly increase the speed of a single sequential read? You can't just read half from one drive, half from the other, you'd always have heads seeking and it would no longer be a sequential read. -ryan