From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: Re: [PATCH 1/4] md: Factor out RAID6 algorithms into lib/ Date: Sat, 18 Jul 2009 12:53:36 +0100 Message-ID: <1247918016.22313.138.camel@macbook.infradead.org> References: <1247494302.19180.268.camel@macbook.infradead.org> <4A5F6590.9000006@zytor.com> <4A608913.1060808@redhat.com> <4A6096A0.5050501@zytor.com> <4A609A52.7070506@redhat.com> <4A609B72.2010901@zytor.com> <4A609CFA.2060707@redhat.com> <4A609D8D.8050501@zytor.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: Ric Wheeler , Dan Williams , chris.mason@oracle.com, linux-btrfs@vger.kernel.org, neilb@suse.de, linux-raid@vger.kernel.org To: "H. Peter Anvin" Return-path: In-Reply-To: <4A609D8D.8050501@zytor.com> List-ID: On Fri, 2009-07-17 at 11:49 -0400, H. Peter Anvin wrote: > Ric Wheeler wrote: > >> > >> The bottom line is pretty much this: the cost of changing the enco= ding > >> would appear to outweigh the benefit. I'm not trying to claim the = Linux > >> RAID-6 implementation is optimal, but it is simple and appears to = be > >> fast enough that the math isn't the bottleneck. > >=20 > > Cost? Thank about how to get free grad student hours testing out th= ings=20 > > that you might or might not want to leverage on down the road :-) > >=20 >=20 > Cost, yes, of changing an on-disk format. Personally, I don't care about that -- I'm utterly uninterested in the legacy RAID-6 setup where it pretends to be a normal disk. I think that model is as fundamentally wrong as flash devices making the similar pretence. I'm only interested in what we can use directly within btrfs -- and ideally I do want something which gives me an _arbitrary_ number of redundant blocks, rather than limiting me to 2. But the legacy code is good enough for now=C2=B9. When I get round to wanting more, I was thinking of lifting something like http://git.infradead.org/mtd-utils.git?a=3Dblob;f=3Dfec.c to start with, and maybe hoping that someone cleverer will come up with somethin= g better. The less I have to deal with Galois Fields, the happier I'll be. --=20 David Woodhouse Open Source Technology Centr= e David.Woodhouse@intel.com Intel Corporatio= n =C2=B9 Well, kind of. The xor_blocks() function will silently screw you= over if you ask it to handle more than 5 blocks at a time. -- 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