From mboxrd@z Thu Jan 1 00:00:00 1970 From: John McMonagle Subject: optimum blockdev --setra settings Date: Mon, 18 Apr 2005 20:55:05 -0500 Message-ID: <426464F9.5040301@advocap.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Anyone establish optimum blockdev --setra settings for raid on a 2.6 kernel? There has been some discussions on the lvm mailing list. In the case of lvm on raid sounds like it's best to use 0 on the md and disk devices and something around 1024 and 4096 on the lvm devices. It seems make some sense that it can cause a lot of unneeded reads particularly if you have a lot of layers and/or a lot of raid5 drives. My experiments have been inconclusive. At least it seems that setting read ahead to 0 on the low level devices has no penalty. John