September 14, 2011 - 6:59pm
Traditional RAID is designed to protect whole disks with block-level redundancy. An array of disks is treated as a RAID group, or protection domain, that can tolerate one or more failures and still recover a failed disk by the redundancy encoded on other drives. The RAID recovery requires reading all the surviving blocks on the other disks in the RAID group to recompute blocks lost on the failed disk. As disks have increased capacity by 40% to 100% per year, their bandwidth has not increased substantially.