Analysis of Reliability Dynamics of SSD RAID

• Published in: IEEE transactions on computers Vol. 65; no. 4; pp. 1131 - 1144
• Main Authors: Li, Yongkun, Lee, Patrick P.C., Lui, John C.S.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.04.2016; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Aging; Arrays; Ash; Disk drives; Error analysis; Numerical models; Reliability; Transient analysis; CTMC; transient analysis; RAID; reliability; Solid-state drives
• ISSN: 0018-9340; 1557-9956
• DOI: 10.1109/TC.2014.2349505

Solid-state drives (SSDs) have been widely deployed in desktops and data centers. However, SSDs suffer from bit errors, and the bit error rate is time dependent since it increases as an SSD wears down. Traditional storage systems mainly use parity-based RAID to provide reliability guarantees by striping redundancy across multiple devices, but the effectiveness of traditional RAID schemes in SSDs remains debatable. In particular, an open problem is how different parity distributions over multiple devices influence the reliability of an SSD RAID array. That is, should we evenly distribute patsaverties as suggested by conventional wisdom, or unevenly distribute parties as recently proposed for SSD RAID? To address this fundamental problem, we propose the first analytical model to quantify the reliability dynamics of an SSD RAID array as it ages. Specifically, we develop a "non-homogeneous" continuous time Markov chain model, and derive the transient reliability solution. We validate our model via trace-driven simulation and conduct numerical analysis to analyze the reliability dynamics of SSD RAID arrays subject to different parity distributions, error rates, and SSD array configurations. Our model enables system practitioners to decide the appropriate parity distribution based on their reliability requirements.