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Appendix A: Introduction to SAS ● 61
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 61), you can
create large configurations.
Direct-Attach Connections
In a direct-attach connection, SAS or SATA disk drives are connected directly to a SAS
controller with SAS cables. One disk drive is connected to one SAS connector with one SAS
cable or multiple disk drives are connected to one SAS connector with one fan-out cable. The
figure on page 31 shows an example of direct-attach connections.
The number of direct-connected disk drives is limited to the number of phys supported by the
SAS controller.
Note:
There may be multiple phys within a single connector. See page 60.
Backplane Connections
In a backplane connection, disk drives and SAS controllers are connected to and communicate
with each other through a system backplane. The figure on page 31 shows an example of
backplane connections.
There are two types of backplane connections, passive and active. When connecting to either
backplane, it’s important to properly connect your disk drive LEDs in order to identify disk
drive conditions. See About Your HostRAID Controller on page 14 for your RAID controller
Activity LED connections and locations.
When connecting to a backplane, the Adaptec Storage Manager enables you to manage your
system disk drives, see Next Steps on page 34.
The number of end devices is limited to the number of slots available on the backplane. For
example, the Adaptec S50 enclosure, which contains an expander, is a backplane connection
that supports up to 12 SAS or SATA disk drives.
Some backplanes support daisy-chain expansion to other backplanes. For example, you can
daisy-chain up to nine Adaptec S50 enclosures to a single SAS controller in a host system.
SAS Expander Connections
A SAS expander device literally expands the number of end devices that you can connect
together. Expander devices, typically embedded into a system backplane (see page 31), support
large configurations of SAS end devices, including SAS controllers and SAS and SATA disk
drives. With expander devices, you can build large and complex storage topologies.
There are two types of SAS expanders: fanout expanders and edge expanders. Each performs a
different role in a storage system. (For more information about how SAS expanders work, refer
to the STA Web site at www.scsita.org.)
You can connect up to 128 SAS ports to an edge expander. (A single edge expander can
therefore support up to 128 SAS addresses.)