From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keld =?iso-8859-1?Q?J=F8rn?= Simonsen Subject: Re: [PATCH 00/18] Assorted md patches headed for 2.6.30 Date: Thu, 12 Feb 2009 18:44:22 +0100 Message-ID: <20090212174422.GA20703@rap.rap.dk> References: <20090212031009.23983.14496.stgit@notabene.brown> <20090212081148.GD9439@rap.rap.dk> <12039e3b9172d1a1347b8396cab59f11.squirrel@neil.brown.name> <20090212095305.GB11981@rap.rap.dk> <780b8d5e33de8ec127222529e84f6026.squirrel@neil.brown.name> <7a329d910902120728u146e7cddk6e7d990668c16345@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <7a329d910902120728u146e7cddk6e7d990668c16345@mail.gmail.com> Sender: linux-raid-owner@vger.kernel.org To: Wil Reichert Cc: NeilBrown , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Thu, Feb 12, 2009 at 07:28:59AM -0800, Wil Reichert wrote: > On Thu, Feb 12, 2009 at 2:45 AM, NeilBrown wrote: > > On Thu, February 12, 2009 8:53 pm, Keld J=F8rn Simonsen wrote: > >> On Thu, Feb 12, 2009 at 08:21:12PM +1100, NeilBrown wrote: > >>> On Thu, February 12, 2009 7:11 pm, Keld J=F8rn Simonsen wrote: > >>> > On Thu, Feb 12, 2009 at 02:10:10PM +1100, NeilBrown wrote: > >>> >> Comments and testing very welcome. > >>> > > >>> > I would rather have functionality to convert raid10 to raid5. > >>> > raid1 should be depreciated, as raid10,n2 for all purposes is t= he same > >>> > but better implementation and performance, and raid10,f2 and ra= id10,o2 > >>> > are even better. Nobody should use raid1 anymore. > >>> > >>> That is a fairly simplistic view. > >> > >> It was also formulated to provoke some thoughts. > >> > >>> raid1 supports --write-mostly and --write-behind which raid10 is > >>> unlikely > >>> ever to support. > >> > >> why? > >> > >> Anyway would it not be possible that this functionality be impleme= nted > >> for raid10,n2? > > > > It would be possible, but it might not be sensible. > > > > write-mostly and write-behind only really make sense when you have = the > > clear distinction between drives that raid1 gives you. > > These options don't make sense for raid10 in general. Only in very= specific > > layouts. > > If you like, raid1 is an implementation of a specific raid10 layout= , > > where it makes sense to add some extra functionality. > > > >> > >> Some code to grow raid10 would also be desirable. Maybe it is some= of > >> the same operations that need to be applied: getting the old data = in, > >> have it restructured for the new format, in a safe way, and possib= ly > >> with the help of an extra disk, or possibly not. It sounds non-tri= vial > >> to me too. > > > > What particular growth scenarios are you interested it? > > Just adding a drive and restriping onto that? i.e keep that > > same nominal layout but increase 'raid-disks'? > > > > That would be quite similar to the raid5 grow operation so it shoul= dn't > > be too hard to achieve. > > A 'grow' which changed the layout (e.g. near to far) would be a lot > > harder. >=20 > I'd previously seen the wikipedia article regarding Linux RAID10 and > its mention of the 3 disk case. Out of academic curiousity, how does > the 2 disk RAID10 work? Is it just a matter of have 2 identical > volumes and reading subsequent stripes from the alteranate drives? O= r > is the algorithm more complicated? There are 3 different layouts for raid10: near, far and offset. Basically raid10 with 2 disks works as RAID 1 - and "near" and linux raid1 is almost equivalent. far and offset has somewhat different placements of blocks on the disks, which should lead to faster operatio= n for some common tasks. best regards keld -- 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