User`s guide

Chapter A: Introduction to Serial Attached SCSI (SAS) ● 63
What do SAS Cables Look Like?
Internal SAS cables are narrower than internal parallel SCSI cables. The connectors vary in size
depending on the number of links they support, from single link connectors to 4-wide (or
larger) connectors. Internal fan-out cables (shown in the next figure) let you attach four disk
drives to a single 4-wide connector.
An example of some internal SAS cables and an external SAS cable are shown in the figure
above.
How are Disk Drives Identified in SAS?
In the BIOS and in the management utilities (see page 52), disk drives are identified with
numbers in this format:
XX:YY:ZZ
where XX is the disk drive count number, YY is the enclosure number, and ZZ is the slot
number (within the enclosure). If the disk drive is not installed in an enclosure, a double
dashes (--) appear instead of YY and ZZ (for instance, 01:--:--).
In parallel SCSI, XX is the disk drive’s channel number, YY is the target number, and ZZ is the
logical unit number (LUN).
What are the SAS Connection Options?
You can connect end devices to each other through direct cable connections and through
backplane connections. When you use one or more expander devices (see page 64), you can
create large configurations.
Direct-attach Connections
In a direct-attach connection, SAS or SATA disk drives are connected directly to a SAS card
with SAS cables. One disk drive is attached to one SAS connector with one SAS cable (or
multiple disk drives are attached to one SAS connector with one fan-out cable). The figure on
page 62 shows an example of direct-attach connections.
The number of direct-attached disk drives is limited to the number of phys supported by the
SAS card. (Note that there may be multiple phys within a single connector. See page 63.)
4x wide-to-4x wide internal SAS cable
Internal SAS-to-SATA fan-out cable (SAS-to-SAS fan-out cables are
also available)
External SAS cable