Adaptec 58300 - SAS Storage Controller 300 MBps Installation And User Manual

Also see for 48300: Installation and user guide Datasheet

Contents

Adaptec 58300 - SAS Storage Controller 300 MBps Installation And User Manual Manual pdf 52 page image

Appendix A: Introduction to SAS ● 52Terminology Used in This ChapterFor convenience, SAS HostRAID controllers are referred to generically in this chapter as SAScards. HBAs, HostRAID controllers, disk drives, and external disk drive enclosures are referredto as end devices and expanders are referred to as expander devices.For convenience, this chapter refers to end devices and expander devices collectively as SASdevices.What is SAS?Legacy parallel SCSI is an interface that lets devices such as computers and disk drivescommunicate with each other. Parallel SCSI moves multiple bits of data in parallel (at the sametime), using the SCSI command set.SAS is an evolution of parallel SCSI to a point-to-point serial interface. SAS also uses the SCSIcommand set, but moves multiple bits of data one at a time. SAS links end devices throughdirect-attach connections, or through expander devices.SAS cards can typically support up to 128 end devices and can communicate with both SASand SATA devices. (You can add 128 end devices—or even more—with the use of SASexpanders. See page 55.)Although you can use both SAS and SATA disk drives in the same SAS domain (see page 55),Adaptec recommends that you not combine SAS and SATA disk drives within the same array orlogical drive. The difference in performance between the two types of disk drives may adverselyaffect the performance of the array.Data can move in both directions simultaneously across a SAS connection (called a link—seenext section). Link speed is 600 MB/sec in full-duplex mode. A SAS card with eight links has amaximum bandwidth of 4800 MB/sec in full-duplex mode.Although they share the SCSI command set, SAS is conceptually different from parallel SCSIphysically, and has its own types of connectors, cables, connection options, and terminology, asdescribed in the rest of this chapter.To compare SAS to parallel SCSI, see How is SAS Different from Parallel SCSI? on page 56.How Do SAS Devices Communicate?SAS devices communicate with each other through links. A link is a physical connectionbetween two phys.