Improving Storage System Availability with D-GRAID

Muthian Sivathanu, Vijayan Prabhakaran,
Andrea C. Arpaci-Dusseau, and Remzi H.Arpaci-Dusseau

Computer Sciences Department,
University of Wisconsin Madison
{muthian, vijayan, dusseau, remzi}@cs.wisc.edu

We present the design, implementation, and evaluation of D-GRAID, a gracefully-degrading and quickly-recovering RAID storage array. D-GRAID ensures that most files within the file system remain available even when an unexpectedly high number of faults occur. D-GRAID also recovers from failures quickly, restoring only live file system data to a hot spare. Both graceful degradation and live-block recovery are implemented in a prototype SCSI-based storage system underneath unmodified file systems, demonstrating that powerful ``file-system like'' functionality can be implemented behind a narrow block-based interface.