From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: Increasing maxsect of md devices? Date: Thu, 3 Mar 2011 09:59:29 +1100 Message-ID: <20110303095929.25b800da@notabene.brown> References: <4D6EC3FA.4030809@bartk.us> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4D6EC3FA.4030809@bartk.us> Sender: linux-raid-owner@vger.kernel.org To: Bart Kus Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On Wed, 02 Mar 2011 14:26:02 -0800 Bart Kus wrote: > Hello, > > This seems contradictory: > > jo ~ # blockdev --getiomin /dev/md5 > 524288 > jo ~ # blockdev --getioopt /dev/md5 > 4194304 > jo ~ # blockdev --getmaxsect /dev/md5 > 255 > jo ~ # blockdev --getbsz /dev/md5 > 4096 > jo ~ # blockdev --getss /dev/md5 > 512 > jo ~ # > > Optimal IO size is reported as 4MB (and that is indeed the stripe size), > but maximum sectors per request is only 128kB? How can software do > optimal 4MB IOs with the maxsect limit? Does XFS care about this limit? md/raid doesn't use 'requests' the any maximum is meaningless. raid4/5/6 does have a 'stripe cache' which is a vaguely similar thing. There can sometimes be value in changing that. The devices that the array are built from may have a 'maximum sectors per request', but that probably isn't particularly related to chunk size. BTW, where do you find "maximum sectors per request in only 128kB" in the details you quoted - I don't see it. NeilBrown