A Virtual Tape System Based on Storage Area Networks

摘要

The access speed of tape has become one of the main bottlenecks in backup work, because tape backup systems axe used quite widely. This paper describes the design and implementation of a Virtual Tape System (VTS) based on the Storage Area Network (SAN), and proposes a tape virtualization technology implemented on the SCSI command level. The system controls the SCSI command stream transferred in the SAN precisely. By transforming the SCSI sequential commands for the tape device into the SCSI block commands for the cache disk, the system makes the cache disk appear and function just like a traditional tape library. Hence, the VTS speeds up the backup process, and reduces the backup window. In addition, the VTS is transparent to users, and has broad compatibility with multiple operating systems and various kinds of backup software. When adopting the virtual tape as the primary backup device, the performance lost is less than 2% compared to backups that use the physical disk as the primary backup device. Another testing result showed that the VTS meets the requirements of backup under a SAN environment and supports multiple backup software and operating systems.