Using a shared storage class memory device to improve the reliability of RAID arrays

Storage class memories (SCMs) constitute an emerging class of non-volatile storage devices that promise to be significantly faster and more reliable than magnetic disks. We propose to add one of these devices to each group of two or three RAID level arrays and store on it additional parity data. We show that the new organization can tolerate all double disk failures, between 75 and 90 percent of all triple disk failures and between 50 and 70 percent of all failures involving two disks and the SCM device without incurring any data loss. As a result, the additional parity device increases the mean time to data loss of the arrays in the group it protects by at least 200-fold.