Improving storage system availability with D-GRAID

TLDR

We present the design, implementation, and evaluation of D‑GRAID, a gracefully degrading and quickly recovering RAID storage array. D‑GRAID achieves high availability by aggressively replicating semantically critical data, isolating fault‑prone blocks, and quickly restoring only live file‑system data to a hot spare, all implemented in a prototype SCSI‑based storage system that supports graceful degradation and live‑block recovery behind a narrow block interface. D‑GRAID ensures that most files remain available even when an unexpectedly high number of faults occur, demonstrating powerful file‑system‑like functionality within a semantically smart disk system.

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 unexpectedly high number of faults occur. D-GRAID achieves high availability through aggressive replication of semantically critical data, and fault-isolated placement of logically related data. 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 within a “semantically smart” disk system behind a narrow block-based interface.