Adaptec 2256100-R Installation And User Manual

Also see for 1045: Quick start guide

Contents

Adaptec 2256100-R Installation And User Manual Manual pdf 51 page image

Chapter A: Introduction to SAS l 51Terminology Used in This AppendixFor convenience, SATA/SAS controllers are referred to generically in this appendix as SAScontrollers. HBAs, disk drives, and external disk drive enclosures are referred to as end devicesand expanders are referred to as expander devices.SAS devices collectively refers to end devices and expander devices.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, using theSCSI 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 controllers can typically support up to 128 end devices and can communicate with bothSAS and SATA devices. You can add 128 end devices or even more with the use of SASexpanders. For more information, see SAS Expander Connections on page 54.Although you can use both SAS and SATA disk drives in the same SAS domain, Adaptecrecommends that you not combine SAS and SATA disk drives within the same array or logicaldrive. The difference in performance between the two types of disk drives may adversely affectthe 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 controller with eight linkshas a maximum 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 page 55.