I took a look at your paper. It's magic! :) My head hurts. :( Ok, I understand that 27 disks is the limit. But is that usable? Would it be too slow? The disk IO seems unreasonable with 27 disks. Guy -----Original Message----- From: H. Peter Anvin [mailto:hpa@xxxxxxxxx] Sent: Friday, October 29, 2004 4:32 PM To: Guy Cc: 'Jim Paris'; 'Neil Brown'; linux-raid@xxxxxxxxxxxxxxx Subject: Re: RAID-6: help wanted Guy wrote: > 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! :) See my paper on the subject: http://www.kernel.org/pub/linux/kernel/people/hpa/raid6.pdf > 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? > The limit is 27 disks total, it's imposed by the md system rather than RAID-6; RAID-6's inherent limit is 254+2 (see, again, the paper.) -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
