From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keld =?iso-8859-1?Q?J=F8rn?= Simonsen Subject: Re: wish for Linux MD mirrored raid types Date: Mon, 9 May 2011 21:57:09 +0200 Message-ID: <20110509195708.GA26847@www2.open-std.org> References: <20110506071752.GA22063@www2.open-std.org> <20110508181445.GB7629@maude.comedia.it> <4DC70A44.5050101@meetinghouse.net> <20110509034036.GA17111@www2.open-std.org> <20110509142426.564aae2c@notabene.brown> 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: <20110509142426.564aae2c@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: NeilBrown Cc: Keld =?iso-8859-1?Q?J=F8rn?= Simonsen , Miles Fidelman , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Mon, May 09, 2011 at 02:24:26PM +1000, NeilBrown wrote: > On Mon, 9 May 2011 05:40:36 +0200 Keld J=F8rn Simonsen wrote: >=20 > > 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 w= rote: > > > >>I would like linux MD raid10 functionality to be part of the Li= nux MD > > > >>RAID1 module, and be called raid1. This is in accordance with t= he > > > >then we need rename the current raid1 functionality to 'mirror'.= in > > > >order to avoid further confusion. > > > >besides, current raid10 does not support resizing, so the featur= e > > > >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 rai= d10-far > > in so far it is a raid1 type - say a raid10,f2 with only 2 disks.=20 >=20 > I think you misread SNIA-DDF. >=20 > In DDF, arrays with a PRL (Primary RAID Level) of 1 can have an RLQ (= RAID > level qualifier) of 0 or 1. > RLQ =3D 0 -> RAID1 with 2 devices > RLQ =3D 1 -> RAID1 with 3 devices. >=20 > DDF also devices a PRL of '11' which it calls "RAID-1E" (though this = term > only appears once in the DDFv1.2 spec) >=20 > For PRL =3D 11 there are two options >=20 > RLQ =3D 0 -> Integrated Adjacent Stripe Mirroring > RLQ =3D 1 -> Integrated Offset Stripe Mirroring. >=20 > These correspond to md/raid10 "near2" and "offset2". >=20 > So DDF: RAID-1E corresponds to md: RAID-10 >=20 > So an 'E' rather than a '0'. >=20 > I would not be against allowing mdadm to accept "raid1e" as a synonym= for > 'raid10', and mentioning the alternate name in the documentation woul= d be > entirely appropriate. Yes, I would like that we cocument the correspondance to the SNIA DDF standard, and do other descriptions as you stipulate. > But RAID-1E is not RAID-1. Nor is RAID-10. I see. By "Nor is RAID-10." you mean RAID-1+0 or linux md raid10? What is the difference between RAID-1E and Linux MD raid10? Linux MD raid10 has "far" layout? Linux MD raid10 can have more than 2 copies? More stuff? > >=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, a= nd RAID6. > >=20 > > Yes, Linux MD raid10 is a very distinct type. We should talk with S= NIA to get it > > recognized. > >=20 > > > What say we leave the names alone. Just beause one person is con= fused is=20 > > > no reason to further confuse things. > >=20 > > The confusion is not just one person. The confusion is unbelievable= common,=20 > > and has proven to be very hard to eliminate. If we align with the S= NIA > > standard, and further get the standard to align with us, then we sh= ould > > have a chance in say 5 years to have reduced the confusion consider= ably. >=20 > The world is full of confusion that is hard to eliminate. >=20 > The problem here I think is simply people who do not educate themselv= es, > either because they cannot be bothered, or because they cannot easily= find > the materials. >=20 > The first is not really a fixable problem. > The second we can address. Improve the already-good wiki or add more= text to > the man pages. Have an aim that every general-information question c= an be > answered by simply posting a like or a passage from the man page. >=20 > That would be really worthwhile. >=20 > Changing names around is, I think, less valuable. It is just that I have been around on other web pages for RAID, to improve references to the linux-raid wiki and to correct errors in thei= r description of Linux RAID. Many - maybe most - people that write about Linux RAID have a number of their details wrong. That should be expert= s conveying their expert wisdom to knowledge-hungry users. An example: http://wiki.linuxquestions.org/wiki/RAID#RAID-10 They claim you need 4 disks for MD raid10. Another example is the Germa= n wikipedia page on RAID - which was moderated and the moderator did not accept my edits. This page does not describe Linux MD raid10.=20 I think naming matters. If we could call Linux MD raid10 for raid1e I think much would be achieved in terms of eliminating misunderstandings. 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