SAS: Scalability at a Whole New Level
Video on demand, Tivo, On-line gaming, Digital photography and Videogaphy, Video and audio editing,. E-mail archives new SEC and federal regulations (SEC banes17a-4, Sarbanes- Oxley, HIPAA, etc.) - The increasing need for storage capacity continues down a seemingly endless path, and the timing for Serial Attached SCSI (SAS) couldn’t have been scripted any better. SAS introduces greater storage scalability and the ability to access that storage faster than ever before.
SCSI is Good
Same time back the dominant disk drive interface in the enterprise server and direct-attach storage market was Ultra320 SCSI, a parallel SCSI speed bump that has now end in innovation. As was then announced by the SCSI Trade Association, the next evolution of SCSI technology beyond Ultra320 is SAS. While Ultra320 SCSI offered many benefits over its available I/O interfaces and has served the market well, its physical limitations leave something to be desired as data center clamor for even greater capacity and higher bandwidth, Parallel SCSI is limited to 15 target devices per bus, and a shared bus at that.
Although it has low-voltage differential, SCSI bus is specified to be up to 12 meter in length. A heavily SCSI bus is, in actuality, much shorter. Since its shared bus, the theoretical maximum throughput is 320MB/s, regarding of the number of disk drives attached on that bus.
SAS is better
SAS introduces a new inflation point in I/O storage technology. Its point-to-point architecture provides dedicated links for each end device at 3Gb/s (6Gb/s full duplex). With those dedicated links, a single I/O or drive failure won’t result in a hung bus that prevents the user from accessing the other disk drives as may occur with parallel SCSI. Furthermore, SAS dual-ported disk drive allows connection to more than one host controller, eliminating single-point of failure. Also the ability to aggregate into wide ports adds yet another level of reliability unseen in previous SCSI generation.
To Be Continued....
