Yiying Zhang

Redundant Arrays

Redundant arrays (RAID) technologies are widely used to provide data reliability in the face of device failure. With new types of storage devices and environments, there are new challenges in deploying RAID technologies. We explore problems with redundant arrays in two different environments.

Correlated Failure of Flash-based Arrays

All standard RAID approaches assume that devices do not wear out, and hence distribute work equally among them. Unfortunately, for flash, this approach is not appropriate as the life of flash cell depends on the number of times it is written and cleaned. Hence, identical write patterns to mirrored flash drives introduce a failure dependency in the storage system, increasing the probability of concurrent device failure and hence data loss.

Warped Mirrors are a solution to this endurance problem for mirrored flash devices. By carefully inducing a slight imbalance into write traffic across devices, we intentionally increase the workload of one device in the mirror pair, and thus increase the odds that it will fail first. Thus, with our approach, device failure independence is preserved.

Duplicate-aware Disk Arrays

Primary storage systems contain only moderate degree of duplication and do not benefit greatly from deduplication. Instead of removing duplicates, we propose a duplication aware disk array (DADA), which recognizes and keeps duplicate contents on disks and make use of its knowledge of duplicates to improve the reliability and availability of disk arrays in various ways. First, DADA can be used to reduce the time spent on disk scrubbing to detect latent sector errors (LSE). Second, DADA reduces RAID reconstruction time during recovery. Finally, DADA provide better reliability than a default RAID array using its knowledge of data duplication.

Related Publications

Warped Mirrors for Flash
Yiying Zhang, Andrea C. Arpaci-Dusseau, Remzi H. Arpaci-Dusseau
Proceedings of the 29th IEEE Conference on Massive Data Storage (MSST '13)

Duplicate-aware Disk Arrays
Vijayan Prabhakaran, Yiying Zhang
US Patent #20120226936

DADA: Duplication Aware Disk Array
Yiying Zhang, Vijayan Prabhakaran
Poster at the 9th Conference on File and Storage Technologies (FAST 2011)