Interestingly, I was just browsing this paper http://www.cs.utk.edu/%7Eplank/plank/papers/CS-05-569.html which appears to be quite on-topic for this discussion. I admit my eyes glaze over during intensive math discussions but it appears tuned RS might not be as horrible as you'd think since apparently state-of-the-art now provides tricks to avoid the Galois Field operations that used to be required. The thought that came to my mind was "how does md's RAID-6 personality compare to EVENODD coding?" Wondering if my home server will ever have enough storage for these discussions to become non-academic for me, :-) Scott -----Original Message----- From: linux-raid-owner@xxxxxxxxxxxxxxx [mailto:linux-raid-owner@xxxxxxxxxxxxxxx] On Behalf Of H. Peter Anvin Sent: Thursday, December 29, 2005 1:41 PM To: linux-raid@xxxxxxxxxxxxxxx Subject: Re: Adding Reed-Solomon Personality to MD, need help/advice Followup to: <dlsh2c$2h0$1@xxxxxxxxxxxxx> By author: "Mario 'BitKoenig' Holbe" <Mario.Holbe@xxxxxxxxxxxxx> In newsgroup: linux.dev.raid > > Hello, > > Nathan Lewis <nathapl@xxxxxxxxxxxxxx> wrote: > > As part of my Master's thesis, I am working on adding a Reed-Solomon > > personality to the existing linux RAID structure and I would like some > > Is there any progress in implementing a generic Reed-Solomon personality > in MD since this mail from 31 Jan 2004? > Regarding the intention-question... for me, personally, it would be the > logical step inbetween raid5 resp. raid6 with survival of 1 resp. 2 > simultaneous disk failures and raid10 with survival of n/2 simultaneous > disk failures. RaidRS would give users the chance to configure > redundancy and thus survivability exactly on their demands. > This would especially make sense when I see the raid5 configurations > with 14 and more devices which some users refer to on this list. > To be honest, I was thinking about such a personality myself, too, and > then was crawling the list's archive. > It's not really in-between; generic RS RAID would be many times slower than either; however, unlike raid10 it could survive *any* m failures where m is the number of redundancy drives. The fundamental problem is that generic RS requires table lookups even in the common case, whereas RAID-6 uses shortcuts to substantially speed up the computation in the common case. RAID-6 is an important corner of the problem space, since it deals with the unfortunately fairly common problem of "disk failure discovered during recovery" with RAID-5. That doesn't mean there couldn't be a problem space where it would make sense (in fact, on the contrary), but it's still a substantial engineering effort that would have to be justified. Heck, I might even be persuaded to look for generic RS shortcuts if someone tempted me enough... -hpa - 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 - 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
