On Wednesday November 13, hpa@zytor.com wrote: > > DISKS ------------------------------------> > 0 4 8 12 PARITY > 1 5 9 13 PARITY > 2 6 10 14 PARITY > 3 7 11 15 PARITY > > If you only write blocks 0-3 you *have* to read in the 12 data blocks > and write out all 4 parity blocks, whereas in RAID-3 you can get away > with only writing 5 blocks. [Well, technically you could also do a > read-modify-write on the parity, since parity is linear. This would > greatly complicate the code.] We do read-modify-write if it involves fewer pre-reads than reconstruct-write. so in the above scenario, writing blocks 0,1,2,3 would cause a pre-read of those blocks and the 4 parity blocks, and then all 8 blocks would be re-written. NeilBrown - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
