h as the Small Computer System Interface (SCSI) bus. Its high data trans- fer rate, low latency, and reliability account for its wide-scale success in coupling computers with a plethora of storage devices. Magnetic disks are the primary online storage medium. Tapes are considered more of a backup and archiving medium. Disk storage is usually found in one of two physical organizations: just a bunch of disks (JBOD) and redundant array of independent (or inexpensive) disks (RAID). On one hand, JBOD storage devices are usually individual, independent disks situated inside a cabinet and accessible individually by a server. They do not provide cache memory (disk buffering) for higher performance or an intelligent controller that allows operations such as data striping (replicating data on different disks) or parity checking for reliability. RAID storage devices, on the other hand, are con- trolled by such a controller (along with lots of memory) and provide functionality such as parity checking, data striping across drives, and even mirroring of critical data across multiple arrays for fault tolerance. Compared to JBOD, RAID provides larger storage capacity, enhanced availability, and significantly improved performance. SCSI emerged as an 8-bit parallel bus in 1979. The SCSI Architecture Model (SAM-2), which is part of the National Committee for Information Technology Standards (NCITS) T10 standard, has cre- ated a layered model for SCSI implementation. The SCSI-3 command set converts the logical layer into a packet-based format, which can be transmitted over a network. As the protocol has evolved, we now have a serial SCSI as a layered, well-structured architecture of protocols that enables services to be requested from storage devices at a distance and over networks. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. STORAGE NETWORK PROCESSORS (SNP