From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: wish for Linux MD mirrored raid types Date: Mon, 9 May 2011 14:24:26 +1000 Message-ID: <20110509142426.564aae2c@notabene.brown> References: <20110506071752.GA22063@www2.open-std.org> <20110508181445.GB7629@maude.comedia.it> <4DC70A44.5050101@meetinghouse.net> <20110509034036.GA17111@www2.open-std.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20110509034036.GA17111@www2.open-std.org> Sender: linux-raid-owner@vger.kernel.org To: Keld =?ISO-8859-1?B?Svhybg==?= Simonsen Cc: Miles Fidelman , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Mon, 9 May 2011 05:40:36 +0200 Keld J=F8rn Simonsen wrote: > On Sun, May 08, 2011 at 05:25:24PM -0400, Miles Fidelman wrote: > > Luca Berra wrote: > > >On Fri, May 06, 2011 at 09:17:52AM +0200, Keld J=F8rn Simonsen wro= te: > > >>I would like linux MD raid10 functionality to be part of the Linu= x MD > > >>RAID1 module, and be called raid1. This is in accordance with the > > >then we need rename the current raid1 functionality to 'mirror'. i= n > > >order to avoid further confusion. > > >besides, current raid10 does not support resizing, so the feature > > >should be added before ditching 'mirror' > > > > >=20 > > The current md RAID1 does exactly what RAID1 is supposed to do. >=20 > I changed my mind a little. >=20 > I think we should follow SNIA wrt. RAID1 - all that SNIA would say is > RAID1 we also should be able to do as RAID1 - that would include > raid10-offset which directly was implemented in the Linux kernel > because of the SNIA RAID1 specification. It should also include raid1= 0-far > in so far it is a raid1 type - say a raid10,f2 with only 2 disks.=20 I think you misread SNIA-DDF. In DDF, arrays with a PRL (Primary RAID Level) of 1 can have an RLQ (RA= ID level qualifier) of 0 or 1. RLQ =3D 0 -> RAID1 with 2 devices RLQ =3D 1 -> RAID1 with 3 devices. DDF also devices a PRL of '11' which it calls "RAID-1E" (though this te= rm only appears once in the DDFv1.2 spec) =46or PRL =3D 11 there are two options RLQ =3D 0 -> Integrated Adjacent Stripe Mirroring RLQ =3D 1 -> Integrated Offset Stripe Mirroring. These correspond to md/raid10 "near2" and "offset2". So DDF: RAID-1E corresponds to md: RAID-10 So an 'E' rather than a '0'. I would not be against allowing mdadm to accept "raid1e" as a synonym f= or 'raid10', and mentioning the alternate name in the documentation would = be entirely appropriate. But RAID-1E is not RAID-1. Nor is RAID-10. >=20 > Then we should keep the raid10 stuff. >=20 > > The md RAID10 is a very specific, and unique approach that has=20 > > similarities to, but is distinct from, RAID1+0, RAID0+1, RAID5, and= RAID6. >=20 > Yes, Linux MD raid10 is a very distinct type. We should talk with SNI= A to get it > recognized. >=20 > > What say we leave the names alone. Just beause one person is confu= sed is=20 > > no reason to further confuse things. >=20 > The confusion is not just one person. The confusion is unbelievable c= ommon,=20 > and has proven to be very hard to eliminate. If we align with the SNI= A > standard, and further get the standard to align with us, then we shou= ld > have a chance in say 5 years to have reduced the confusion considerab= ly. The world is full of confusion that is hard to eliminate. The problem here I think is simply people who do not educate themselves= , either because they cannot be bothered, or because they cannot easily f= ind the materials. The first is not really a fixable problem. The second we can address. Improve the already-good wiki or add more t= ext to the man pages. Have an aim that every general-information question can= be answered by simply posting a like or a passage from the man page. That would be really worthwhile. Changing names around is, I think, less valuable. Thanks, NeilBrown -- 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