Improving Storage System Availability with D-GRAID

Abstract

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 unexpectdly 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, demonstrating that powerful "file-system like" functionality can be implemented behind a narrow block-based interface.