Reliability and Security of D2D Backup Storage Systems using SATA Drives
Magnetic tape has long been used to backup computer information, customarily during dedicated, low use, 'overnight windows' when tape backup programs could be run without interfering with user applications. Over time these windows have shrunk to near non-existence due to the globalization of business through its use of the Internet and the World Wide Web. While tape system speeds have accelerated and tape capacities have increased, they have not keep pace with the demand for shorter backup windows, quicker restoration requirements, and the rapidly escalating volume of disk drive data being backed up. At the same time, the cost of PC disk drives ("ATA" computer interface) has dropped to be competitive with tape, and disk-to-disk (D2D) backup has become popular, particularly using the new Serial ATA (SATA) PC drives. A D2D system can run at the full speed of disk, and can use the higher capacity of PC disk drives (up to 400 Gbytes today), because backup is primarily serial data storage not needing the high high random access speed of the enterprise storage systems being backed up (which get high random access speed by running many smaller capacity disks in parallel). The current interest in SATA D2D backup is of concern because these are PC drives sold with narrow profit margins that limit drive reliability.
This paper addresses the fact that the reliability of SATA PC drives is inherently lower than enterprise-class drives (SCSI and Fiber Channel "SCSI/FC"). Methods are proposed for SATA storage system designers to achieve high system level reliability by requiring appropriate SATA drive reliability testing, by increased RAID redundancy, and by system management of drive failure warnings. A method is proposed for maintaining user data security in removable D2D archival drives.