From mboxrd@z Thu Jan 1 00:00:00 1970 From: Namhyung Kim Subject: Re: [PATCH v2 1/5] md/raid10: optimize read_balance() for 'far offset' arrays Date: Wed, 15 Jun 2011 21:25:33 +0900 Message-ID: <1308140733.1358.41.camel@leonhard> References: <1308103324-2375-1-git-send-email-namhyung@gmail.com> <1308103324-2375-2-git-send-email-namhyung@gmail.com> <20110615065144.GA28174@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: <20110615065144.GA28174@www2.open-std.org> Sender: linux-raid-owner@vger.kernel.org To: Keld =?ISO-8859-1?Q?J=F8rn?= Simonsen Cc: Neil Brown , linux-raid@vger.kernel.org List-Id: linux-raid.ids 2011-06-15 (=EC=88=98), 08:51 +0200, Keld J=C3=B8rn Simonsen: > On Wed, Jun 15, 2011 at 11:02:00AM +0900, Namhyung Kim wrote: > > If @conf->far_offset > 0, there is only 1 stripe so that we can tre= at > > the array same as 'near' arrays. >=20 > does it also work with more than 2 copies - eg 3 copies? > I think the original code just takes the available data blocks with t= he=20 > lowest address. >=20 Hi, Let me clarify this: AFAIK, 'far offset' array saves redundant data in the diagonally adjacent chunk/disk, so it could be roughly thought as 'raid0' array with reduced size - just ignore redundant chunks here. It was my mistake considering it as 'near' array. :( Therefore, it makes more sense distributing reads over the array based on some criteria - here, the address of starting sector - like RAID0 does. Now I see that the same goes to the 'far copies' array exactly, s= o the original code is correct. Thanks. --=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