Oracle SG-XPCIESAS-R-INT-Z, Installation Manual

Page: 118 / 148

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 .