From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wil Reichert Subject: Re: [PATCH 00/18] Assorted md patches headed for 2.6.30 Date: Thu, 12 Feb 2009 07:28:59 -0800 Message-ID: <7a329d910902120728u146e7cddk6e7d990668c16345@mail.gmail.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <780b8d5e33de8ec127222529e84f6026.squirrel@neil.brown.name> Sender: linux-raid-owner@vger.kernel.org To: NeilBrown Cc: =?UTF-8?Q?Keld_J=C3=B8rn_Simonsen?= , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Thu, Feb 12, 2009 at 2:45 AM, NeilBrown wrote: > On Thu, February 12, 2009 8:53 pm, Keld J=C3=B8rn Simonsen wrote: >> On Thu, Feb 12, 2009 at 08:21:12PM +1100, NeilBrown wrote: >>> On Thu, February 12, 2009 7:11 pm, Keld J=C3=B8rn 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 the= same >>> > but better implementation and performance, and raid10,f2 and raid= 10,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 implement= ed >> 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 th= e > clear distinction between drives that raid1 gives you. > These options don't make sense for raid10 in general. Only in very s= pecific > 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 o= f >> 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 possibly >> with the help of an extra disk, or possibly not. It sounds non-trivi= al >> 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 shouldn= 't > be too hard to achieve. > A 'grow' which changed the layout (e.g. near to far) would be a lot > harder. 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? Or is the algorithm more complicated? Wil -- 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