[. . . ] SAS will ultimately replace traditional Parallel SCSI drives, which have been around for the better part of two decades and have reached their performance limit. Parallel interfaces have become technologically more challenging as their respective clock frequencies have increased to keep pace with the bandwidth requirements of their attached storage devices. Improvements expanded it to a 16-bit data bus, leaping the performance from 10Mb per second to 20Mb per second without increasing the clock speed. In 2001, the maximum clock speed for SCSI attained 320 MHz (maximum burst rate of 320MB per second) after overcoming significant obstacles such as signal distortion ("cross-talk") and skewing errors. [. . . ] The 4Gb FC interface is backward compatible with 2 Gb FC. Figure 2. R/Evolution SAS Architecture SAS and FC Similarities Both FC and SAS offer the maturity, richness, depth and scope of the SCSI command set. They are differentiated by their drive-to-drive connectivity, their inter-box connectivity and their addressability. FC's combination of shared media access, data rate, optical support and fabric compatibility has made it the interface of choice for SANs and high-speed switching environments. data intensive transactional applications. For example, a SAS connection on a JBOD system can support a theoretical maximum of 1, 200 MB/s (see figure 2). SAS is also used as a high performance yet cost-effective expansion port to daisy chain to another SAS subsystem. SAS drives, like Fibre Channel drives, are designed for the rigors of enterprise use and heavy loads, have MTBF ratings in excess of 1 million hours and warranties up to 5 years. Both SAS and FC drives are engineered for rugged enterprise duty, and every component (drive motor, spindle, actuator, firmware, etc. ) is specifically designed and manufactured for that rigorous use. SAS drives also safeguard data integrity via their comprehensive verification/error correction capabilities. 5 SAS & Fibre Channel - Compared SAS drive-based subsystems also support the following: "Active-active controllers for failover "Redundant host connections that could be SAS, Fibre Channel or iSCSI "Fibre Channel or iSCSI "Redundant hot swappable power, cooling, controllers and disks "Enclosure services and the same RAID and software capabilities found in Fibre Channel and SCSI-based arrays. Given the superior price/performance ratio and reliability equivalence to FC drives, unit sales for SAS drives will grow significantly in the next few years. Overall unit shipments for SAS will grow modestly, while FC drives units will remain relatively flat with SATA drives showing continued growth as well. The decision WAS simple: choose FC hard drives for applications that require any type of performance; then choose SATA hard drives when low cost storage and/or high capacity is required. The addition of SAS has increased the options IT managers have to solve their disk storage challenges providing an alternative solution for high performance applications with an attractive price/performance. Fibre Channel disk drives, as Gartner and IDC have forecasted will be found installed in applications where performance requirements exceed the priceto-performance attributes SAS offers. SATA will continue to be the storage choice for economic driven applications. devices do, essentially increasing data throughput and improving the ability to locate and fix disk failures. SAS inherits its command set from parallel SCSI, its frame formats from Fibre Channel, and its physical characteristics from Serial ATA. Figure 3 SAS Expander SAS Benefits Relative to parallel SCSI, Serial Attached SCSI drives (SAS) will have much more throughput and higher levels of performance. Most notably, SAS drives can send and receive data simultaneously or serially. SAS drives support speeds of up to 15, 000 RPM; double that of SATA drives. From a cost perspective, SAS drives will be priced similarly to Parallel SCSI drives, and be less expensive than Fibre Channel drives and related infrastructure. However, SAS will become the drive of choice for most performance related applications. In addition, each 3 Gb high performance SAS drive (10K rpm or 15K rpm) is connected to a 3Gb drive connection, providing more than enough bandwidth for the highest performing drives. [. . . ] While offering alternatives to more costly high-end systems, SAS will provide a new tier of storage in the midrange. SAS will be the foundation of high-end enterprise storage over the next several years. It's the key ingredient to enabling new approaches to tiered storage. systems (except for high-end SANs) · Many applications will support SAS and SATA drives within the same system As the sophistication of evaluating the value of data improves, IT managers will continue to scrutinize the requirement for data to be always available at extremely high data rates. While the FC network continues to be a mainstay, expensive ultra high performance Fibre Channel disk drives will apply to only niche applications. [. . . ]