Could you translate this into English? P' = P + D_n + D_n' Q' = Q + g^n * D_n + g^n * D_n' I understand this much: P =old parity D_n =old data block(s) P' =new parity D_n' =new data block(s) But is "+" = xor? I am lost on this one: Q' = Q + g^n * D_n + g^n * D_n' With the parity (xor) it can be done by the bit, so an example is easy. Can Q be done by the bit, and if so, could you give an example? If it takes more than 10 minutes, just tell me it is magic! :) Also, on a related subject.... I have a 14 disk RAID5 with 1 spare. Once RAID6 seems safe and stable I had hoped to convert to a 15 disk RAID6. Is 15 disks too much for RAID6? Any idea what a reasonable limit would be? Thanks, Guy -----Original Message----- From: linux-raid-owner@xxxxxxxxxxxxxxx [mailto:linux-raid-owner@xxxxxxxxxxxxxxx] On Behalf Of Jim Paris Sent: Friday, October 29, 2004 3:22 PM To: H. Peter Anvin Cc: Guy; 'Neil Brown'; linux-raid@xxxxxxxxxxxxxxx Subject: Re: RAID-6: help wanted > >I think they can both be updated with read-modify-write: > > > >P' = P + D_n + D_n' > >Q' = Q + g^n * D_n + g^n * D_n' > > It's not a matter of cache-trashing, it's a matter of the fact that very > few CPUs have any form of parallel table lookup. It could be done with > dynamic code generation, but that's a whole ball of wax on its own. Why dynamic? Are there problems with just pregenerating all 256 optimized codepaths? -jim - 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
