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Disk Drive Specifications
Disk storage drives are improving in all aspects of reliability and performance and are being led by the widespread usage of SATA, SAS, SCSI, and FC. These drive types are not the same and are used for different storage applications. The growing appeal of SATA (Serial Advanced Technology Architecture) disk subsystems started with its successful entry into the desktop PC and entry-level server industry in 2001. SATA has since replaced its predecessor ATA interface drives, an older and slower but widely used internal desktop interface, as the low-cost drive of choice.
Reliability measured by duty cycle and MTBF is considerably better for SCSI, SAS and Fibre Channel than for SATA drives. The reliability of FC and SATA drives is measured differently. The failure rates of high-performance FC disk drives are based upon 24 hour-per-day, 365 days per year usage - a 100 percent duty cycle. Availability measurements for SATA drives are typically based on four to eight hours' usage per day as the drives are frequently powered on and off. RAID architecture has helped address the impact of more frequent device failures and fueled the usage of SATA beyond the desktop markets and into the data center. FC drives also contain two microprocessors, one to control the servo mechanism and error recovery, and the other to operate command queuing and data transfer. SATA drives contain one processor to handle everything and multiple I/O requests can cause degradation.
With current data rates of 150 to 300 megabytes per second and a roadmap that calls for at least two more generations of SATA reaching 600 megabytes per second, coupled with the low drive cost compared to SCSI, SAS and Fibre Channel, SATA-based disk drives are becoming a somewhat disruptive force in the disk industry. Fibre Channel has a significant distance and connectivity advantage over the other disk interfaces and its increased usage in the late 1990s is the primary reason that SAN switched fabrics gained widespread momentum. In addition, the IP Storage protocols can extend both SCSI and Fibre Channel capabilities over much longer distances using Gigabit Ethernet as a delivery mechanism.
Source: Horison Information Strategies: Storage Navigator
© 2005 Horison
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