Sas Architecture - IBM SAS RAID Series Manual

Figure 6. CCIN 574E PCIe x8 Ext Dual-x4 3 Gb SAS RAID adapter
Related concepts
Chapter 5, "Dual storage IOA configurations," on page 21
You can increase availability using a dual storage I/O adapter (IOA) configuration to connect multiple
controllers to a common set of disk expansion drawers and the included disks and disk arrays.
"Dual storage IOA functions" on page 22
Consider these factors when using dual storage I/O adapter (IOA) functions.

SAS architecture

Serial-attached SCSI (SAS) architecture defines a serial device interconnect and transport protocol that
defines the rules for information exchange between devices.
SAS is an evolution of the parallel SCSI device interface into a serial point-to-point interface. SAS
physical links (phys) are a set of four wires used as two differential signal pairs. One differential signal
transmits in one direction, while the other differential signal transmits in the opposite direction. Data can
be transmitted in both directions simultaneously. Phys are contained in SAS ports which contain one or
more phys. A port is a wide port if there are more than one phy in the port. If there is only one phy in
the port, it is a narrow port. A port is identified by a unique SAS worldwide name (also called SAS
address).
A SAS controller contains one or more SAS ports. A path is a logical point-to-point link between a SAS
initiator port in the controller and a SAS target port in the I/O device (for example a disk). A connection
is a temporary association between a controller and an I/O device through a path. A connection enables
communication to a device. The controller can communicate to the I/O device over this connection by
using either the SCSI command set or the ATA/ATAPI command set depending on the device type.
A SAS expander enables connections between a controller port and multiple I/O device ports by routing
connections between the expander ports. Only a single connection through an expander can exist at any
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SAS RAID controllers for IBM i