Followup to: <[EMAIL PROTECTED]>
By author: "Mario 'BitKoenig' Holbe" <[EMAIL PROTECTED]>
In newsgroup: linux.dev.raid
>
> Hello,
>
> Nathan Lewis <[EMAIL PROTECTED]> 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
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