On Mon, May 09, 2011 at 02:24:26PM +1000, NeilBrown wrote: > On Mon, 9 May 2011 05:40:36 +0200 Keld Jørn Simonsen <keld@xxxxxxxxxx> 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 Jørn Simonsen wrote: > > > >>I would like linux MD raid10 functionality to be part of the Linux MD > > > >>RAID1 module, and be called raid1. This is in accordance with the > > > >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 feature > > > >should be added before ditching 'mirror' > > > > > > > > > > The current md RAID1 does exactly what RAID1 is supposed to do. > > > > I changed my mind a little. > > > > 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 raid10-far > > in so far it is a raid1 type - say a raid10,f2 with only 2 disks. > > I think you misread SNIA-DDF. > > In DDF, arrays with a PRL (Primary RAID Level) of 1 can have an RLQ (RAID > level qualifier) of 0 or 1. > RLQ = 0 -> RAID1 with 2 devices > RLQ = 1 -> RAID1 with 3 devices. > > DDF also devices a PRL of '11' which it calls "RAID-1E" (though this term > only appears once in the DDFv1.2 spec) > > For PRL = 11 there are two options > > RLQ = 0 -> Integrated Adjacent Stripe Mirroring > RLQ = 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 for > 'raid10', and mentioning the alternate name in the documentation would 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? > > > > Then we should keep the raid10 stuff. > > > > > The md RAID10 is a very specific, and unique approach that has > > > similarities to, but is distinct from, RAID1+0, RAID0+1, RAID5, and RAID6. > > > > Yes, Linux MD raid10 is a very distinct type. We should talk with SNIA to get it > > recognized. > > > > > What say we leave the names alone. Just beause one person is confused is > > > no reason to further confuse things. > > > > The confusion is not just one person. The confusion is unbelievable common, > > and has proven to be very hard to eliminate. If we align with the SNIA > > standard, and further get the standard to align with us, then we should > > have a chance in say 5 years to have reduced the confusion considerably. > > 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 find > the materials. > > 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 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. 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 their description of Linux RAID. Many - maybe most - people that write about Linux RAID have a number of their details wrong. That should be experts 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 German wikipedia page on RAID - which was moderated and the moderator did not accept my edits. This page does not describe Linux MD raid10. 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" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
