From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Rabbitson Subject: Raid6 write performance Date: Mon, 19 Jan 2009 08:40:36 +0100 Message-ID: <49742E74.9090502@rabbit.us> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Hi, I am experimenting with raid6 on 4 drives on 2.6.27.11. The problem I am having is that no matter what chunk size I use, the write benchmark always comes out at single drive speed, although I should be seeing double drive speed (read speed is at near 4x as expected). Is there some hidden setting that I am overlooking, or is this a current known limitation of raid6? In contrast if I make a raid5 on these 4 drives, I get the expected 3xdrive write speed, and occasionally 4xdrive linear read speed. When the write test is running, I get about 14% of system cpu a sporadic 40% of iowait and the rest idle at all times (machine is in runlevel 1 so not to screw with results). Anyone has any ideas? Thank you.