From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: [PATCH v2 1/5] md/raid10: optimize read_balance() for 'far offset' arrays Date: Thu, 16 Jun 2011 09:56:07 +1000 Message-ID: <20110616095607.4869fbde@notabene.brown> 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> <1308140733.1358.41.camel@leonhard> <87aadj9n7a.fsf@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <87aadj9n7a.fsf@gmail.com> Sender: linux-raid-owner@vger.kernel.org To: Namhyung Kim Cc: Keld =?ISO-8859-1?B?Svhybg==?= Simonsen , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Wed, 15 Jun 2011 23:35:53 +0900 Namhyung Kim wr= ote: > Namhyung Kim writes: > > 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 = treat > >> > 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 wit= h the=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= =2E It > > was my mistake considering it as 'near' array. :( > > >=20 > I'm confused again. If fo > 0 && fc > 1 && nc > 1 then it turns out t= o > a near array with reduced size, no? Does it still need to be treaded > as RAID0? This would be a mix of near and offset. I'm not at all sure what the "= best" read balancing approach would be. But as I don't think anyone would ev= er actually use it, I don't think it really matters. Thanks, NeilBrown >=20 >=20 > > Therefore, it makes more sense distributing reads over the array ba= sed > > on some criteria - here, the address of starting sector - like RAID= 0 > > does. Now I see that the same goes to the 'far copies' array exactl= y, so > > the original code is correct. > > > > Thanks. > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid"= in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- 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