HP NetServer LXr Pro8 Server Controllers and Mass Storage Devices - Page 3

ZKLWHýSDSHU +3ý 1HW6HUYHUý $FFHVVRULHV Connectivity A SCSI interface is an independent and intelligent local I/O bus. Through this bus a variety of different devices and one or more controllers can communicate and exchange information. The SCSI interface operates independently of the actions of the rest of the MBytes/Sec 90 system. Many types of peripherals can be connected along the bus including tape 80 drives, hard disk drives, scanners, 70 printers, disk array subsystems, and 60 CD-ROM drives. Device performance is a 50 function of the interface data transfer 40 rates and the saturation of the I/O bus. 30 Various levels of performance using a SCSI controller and I/O bus are available 20 (see Figure 2). 10 0 Ultra SCSI Wide Ultra SCSI Wide Ultra2 SCSI (LVD) As SCSI technology has evolved, the server systems benefit by the increased Figure 2. Storage Controller Maximum Transfer Rate performance and capability that the most recent designs provide. The latest step in the evolution of SCSI is Wide Ultra2 SCSI which uses low-voltage differential technology to extend the current SCSI specifications for cable length, transfer speed and maximum number of devices per bus. The continued evolution of the SCSI standard and its on-going implementation in products, make it a cost-effective storage solution, especially for the entry and mid-range level servers. Fibre Channel (FC), another connectivity standard, is making inroads into the high-end Intel-based server market as an alternative to SCSI in configurations in which high availability, storage scalability and configuration flexibility are demanded. Fibre Channel provides the user with several improvements over the current connectivity technologies. The server systems can be cabled over much larger distances, eventually up to 10 kilometers, allowing for mirrored configurations that enhance disaster tolerant scenarios. The server systems will be more scaleable. SCSI supports a maximum of 15 disks per channel while up to 126 disks can be attached to a single Fibre Channel arbitrated loop. Fibre Channel cabling is much easier to use than SCSI cabling since terminators are not required and thin cables with simple connectors replace thick cables with multi-pin connectors. Another characteristic that distinguishes Fibre Channel from SCSI is that it is designed to support a network infrastructure, including hubs and switches. Added to cabling distance, the networking characteristic gives Fibre Channel tremendous flexibility to support not only high availability system configurations but also storage networking applications. 3