From mboxrd@z Thu Jan 1 00:00:00 1970 From: Namhyung Kim Subject: Re: [PATCH/RFC] md/raid10: optimize read_balance() for 'far copies' arrays Date: Wed, 08 Jun 2011 23:39:31 +0900 Message-ID: <87ei349yl8.fsf@gmail.com> References: <1307516445-3208-1-git-send-email-namhyung@gmail.com> <20110608172157.4d6ac2a8@notabene.brown> <877h8w93bw.fsf@gmail.com> <20110608114924.GA10134@www2.open-std.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20110608114924.GA10134@www2.open-std.org> ("Keld =?utf-8?Q?J?= =?utf-8?Q?=C3=B8rn?= Simonsen"'s message of "Wed, 8 Jun 2011 13:49:25 +0200") Sender: linux-raid-owner@vger.kernel.org To: Keld =?utf-8?Q?J=C3=B8rn?= Simonsen Cc: NeilBrown , linux-raid@vger.kernel.org List-Id: linux-raid.ids Keld J=C3=B8rn Simonsen writes: > On Wed, Jun 08, 2011 at 04:42:27PM +0900, Namhyung Kim wrote: >> Still can't understand why we choose the closest-to-the-start disk i= n >> case we could have possible sequencial access on other disk. Probabl= y >> because of the lack of my understanding how md/disk works :( > > the nearest position was the case for the initial implementation of > raid10-far. But this had bad performance for an array with disks of > varying specifications. And also it led to not using the faster > outer sectors. Using the closest-to-beginning gave a spped-up of abou= t > 50 % in some cases. > Hi Keld, Thanks for the explanation. That means lower sectors reside on the oute= r tracks/cylinders in the disk, right? The 50% seems a huge improvement I couldn't stand against. Although my patch tried to choose closest-to-current-head disk if the disk head is in the lowest stripe - in the (similar) hope that it'd be on the outer tracks - I don't have the numbers, so I'll just give up on it. Besides, I just noticed that the rationale behind read_balance() pressumed that all components of the array are traditional disks. If we could detect all/some of them are not (i.e. SSD, etc.), it would be better off using some other criteria for the read balancing IMHO, something like nr_pending? --=20 Regards, Namhyung Kim -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html