On 20/11/13 02:23, John Williams wrote: > On Tue, Nov 19, 2013 at 4:54 PM, Chris Murphy <lists@xxxxxxxxxxxxxxxxx> > wrote: >> If anything, I'd like to see two implementations of RAID 6 dual >> parity. The existing implementation in the md driver and btrfs could >> remain the default, but users could opt into Cauchy matrix based dual >> parity which would then enable them an easy (and live) migration path >> to triple parity and beyond. Andrea's Cauchy matrix is compatible with the existing Raid6, so there is no problem there. I believe it would be a terrible idea to have an incompatible extension - that would mean you could not have temporary extra parity drives with asymmetrical layouts, which is something I see as a very useful feature. > > Actually, my understanding is that Andrea's Cauchy matrix technique > (call it C) is compatible with existing md RAID5 and RAID6 (call these > A). It is only the non-SSSE3 triple-parity algorithm 2^-1 (call it B) > that is incompatible with his Cauchy matrix technique. > > So, you can have: > > 1) A+B > > or > > 2) A+C > > But you cannot have A+B+C Yes, that's right. -- 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
