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 23:35:53 +0900 Message-ID: <87aadj9n7a.fsf@gmail.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <1308140733.1358.41.camel@leonhard> (Namhyung Kim's message of "Wed, 15 Jun 2011 21:25:33 +0900") Sender: linux-raid-owner@vger.kernel.org To: Keld =?utf-8?Q?J=C3=B8rn?= Simonsen Cc: Neil Brown , linux-raid@vger.kernel.org List-Id: linux-raid.ids 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 tr= eat >> > 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 = the=20 >> lowest address. >>=20 > > Hi, > > Let me clarify this: AFAIK, 'far offset' array saves redundant data i= n > 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. :( > I'm confused again. If fo > 0 && fc > 1 && nc > 1 then it turns out to a near array with reduced size, no? Does it still need to be treaded as RAID0? > Therefore, it makes more sense distributing reads over the array base= d > 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,= so > the original code is correct. > > Thanks. -- 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