From mboxrd@z Thu Jan 1 00:00:00 1970 From: Molle Bestefich Subject: Re: Raid 1 disk scheduling Date: Mon, 30 May 2005 10:01:58 +0200 Message-ID: <62b0912f05053001013e2d8e47@mail.gmail.com> References: <20050529190628.46785.qmail@web30501.mail.mud.yahoo.com> Reply-To: Molle Bestefich Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Return-path: In-Reply-To: <20050529190628.46785.qmail@web30501.mail.mud.yahoo.com> Content-Disposition: inline Sender: linux-raid-owner@vger.kernel.org To: dbakker1@yahoo.com Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids David F. Bakker wrote: > I have a server with lots of available RAM (10GB) I > wanted to create an md raid 1 device that would mirror > a large ramdisk (2GB) to a scsi md device. The > thinking here is writes will be just as fast as always > since I/O is sync to both the RAM and hard disk. > However reads should be crazy fast since it should be > coming from the device with the lower latency or the > one that answers first (RAM). It looks like the I/O is > done in a round robin setup. I get amazing reads every > other test (cat'n a file) which seems it is a round > robin scheme. Can this be changed somehow to prefer a > device or use latency instead? Linux should use any available RAM for disk cache. Are you sure that using MD as a disk cache like above is any faster than that?