Adaptec SAS RAID Controllers Instalační příručka stáhnout pdf (Strana 118)

104 Sun StorageTek SAS RAID HBA Installation Guide • March 2010

Terminology Used in This Appendix

For convenience, SAS HBAs and SAS RAID HBAs are referred to generically in this

appendix as SAS cards. HBAs, RAID controllers, disk drives, and external disk drive

enclosures are referred to as end devices and expanders are referred to as expander

devices.

For convenience, this appendix refers to end devices and expander devices

collectively as SAS devices.

About SAS

Legacy parallel SCSI is an interface that lets devices such as computers and disk

drives communicate with each other. Parallel SCSI moves multiple bits of data in

parallel (at the same time), using the SCSI command set.

SAS is an evolution of parallel SCSI to a point-to-point serial interface. SAS also uses

the SCSI command set, but moves multiple bits of data one at a time. SAS links end

devices through direct-attach connections, or through expander devices.

SAS cards can typically support up to 128 end devices and can communicate with

both SAS and SATA devices. (You can add 128 end devices—or even more—with the

use of SAS expanders. See “SAS Expander Connections” on page 109.)

Note – Although you can use both SAS and SATA disk drives in the same SAS

domain (see “SAS Expander Connections” on page 109), do not combine SAS and

SATA disk drives within the same array or logical drive. The difference in

performance between the two types of disk drives may adversely affect the

performance of the array.

Data can move in both directions simultaneously across a SAS connection (called a

link—see “About SAS Device Communication” on page 105). Link speed is 300

MB/sec in half-duplex mode. Therefore, a SAS card with eight links has a bandwidth

of 2400 MB/sec.

Although they share the SCSI command set, SAS is conceptually different from

parallel SCSI physically, and has its own types of connectors, cables, connection

options, and terminology, as described in the rest of this chapter.

To compare SAS to parallel SCSI, see “Differences Between SAS and Parallel SCSI” on

page 110.

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Adaptec SAS RAID Controllers Instalační příručka Strana 118