Appendix A: Introduction to Serial Attached SCSI (SAS)
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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
), 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
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
Backplane Connections
In a backplane connection, disk drives and SAS cards are attached to
and communicate with each other through a system backplane.
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 (connect one to the next) up to nine
Adaptec S50 enclosures to a single SAS card in a host system.
