Compaq ProLiant 1000 Drive technology overview - Page 7

factory and at HP option kitting configuration sites. Product quality data is reviewed on a daily, weekly, and monthly basis. Interconnect technology Various interconnect technologies are used to connect one or more disk drives to a computer system. Technology has transitioned from parallel bus data interfaces (ATA, IDE, and the original SCSI interface) to SATA and SAS serial interfaces in which each drive has its own high-speed serial communication channel to the disk controller. Table 3 lists basic characteristics of SATA and SAS interfaces, which are now on their second generations. Certain capabilities have traditionally been inherent in SAS or SATA, but this is changing. The benefits and constraints of these two interfaces may become blurred. Table 3. Comparison of SAS and SATA interfaces for industry-standard servers 2nd Gen. SATA SAS SAS-2 Architecture point-to-point half duplex serial bus point-to-point full duplex serial bus point-to-point full duplex serial bus Maximum throughput 300 MB/s (3 Gb/s) 300 MB/s (3 Gb/s) 600 MB/s (6 Gb/s) Cable length 1m 6m 10 m Number of devices supported Command set 1 per link 2-6 typical ATA 16,256 (SAS fabric) 512 - 2048 practical Unlimited (SAS fabric) 512 - 2048 practical SCSI SCSI Hot swap support yes yes yes Drive ID Drives supported Optional ID Used for Mgmt. SATA only worldwide unique ID set at factory SAS or SATA (Can be mixed) worldwide unique ID set at factory SAS or SATA (Can be mixed) Serial Attached SCSI (SAS) SAS is generally considered the most cost-effective solution for mission critical, high I/O workload applications, such as business critical databases. Dual ported SAS disk drives provide two activeactive paths to each device. SAS inherits the proven SCSI command set but uses a point-to-point serial interface, with each device connecting directly to a SAS point. The serial interface makes the complete bandwidth of the link available to each device, which greatly increases performance and scalability. In addition, the links are full duplex and can be grouped to further increase bandwidth. First generation SAS supported a link speed of 3 Gb/s. The second (current) generation supports a link speed of up to 6 Gb/s. SAS is built upon the SATA physical characteristics. This means that SATA drives can be used with SAS controllers. In fact, SATA and SAS drives can be mixed in a single enclosure. However, SAS devices cannot be used with SATA controllers. 7