Sas Subsystem For The 5148-21L, 5148-22L, 8247-21L, 8247-22L, 8247-42L, 8284-21A, 8284-22A, 8286-41A, Or 8286-42A; What's New In Sas Subsystem For The 5148-21L, 5148-22L, 8247-21L, 8247-22L, 8247-42L, 8284-21A, 8284-22A, 8286-41A, Or 8286-42A; Sas Architecture - IBM Power System 5148-21L Manual

SAS subsystem for the 5148-21L, 5148-22L, 8247-21L,
8247-22L, 8247-42L, 8284-21A, 8284-22A, 8286-41A, or
8286-42A
Review the Serial-attached SCSI (SAS) subsystem features, configurations, and limitations for the IBM
Elastic Storage Server Management Server (5148-21L), IBM Elastic Storage Server Data Server (5148-22L),
®
IBM Power System S812L (8247-21L), IBM Power System S822L (8247-22L), IBM Power System S824L
(8247-42L), IBM Power System S812 (8284-21A), IBM Power System S822 (8284-22A), IBM Power System
S814 (8286-41A), and the IBM Power System S824 (8286-42A) servers.
What's new in SAS subsystem for the 5148-21L, 5148-22L, 8247-21L,
8247-22L, 8247-42L, 8284-21A, 8284-22A, 8286-41A, or 8286-42A
Read about new or significantly changed information in SAS subsystem for the 5148-21L, 5148-22L,
8247-21L, 8247-22L, 8247-42L, 8284-21A, 8284-22A, 8286-41A, or 8286-42A.
February 2017
Added information for the IBM Power System S812 (8284-21A) servers.
December 2016
Added information for the IBM Elastic Storage Server Management Server (5148-21L) and IBM Elastic
Storage Server Data Server (5148-22L) servers.

SAS architecture

Serial-attached SCSI (SAS) architecture describes a serial device interconnection and transportation
protocol that defines the rules for information exchange between devices.
SAS is an evolution of the parallel Small Computer System Interface (SCSI) device interface into a serial
point-to-point interface. SAS physical links 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. Physical links are contained
in SAS ports, which contain one or more physical links. If there is more than one physical link in the
port, the port is a wide port. If there is only one physical link in the port, it is a narrow port. A port is
identified by a unique SAS worldwide name (also called SAS address).
A SAS adapter contains one or more SAS ports. A path is a logical point-to-point link between a SAS
initiator port in the adapter and a SAS target port in the I/O device (for example, a disk). A connection is
a temporary association between an adapter and an I/O device through a path. A connection enables
communication to a device. The adapter can communicate to the I/O device over this connection by
using either the SCSI command set or the Advanced Technology Attachment (ATA) and Advanced
Technology Attachment Packet Interface (ATAPI) command set depending on the device type.
A SAS expander enables connections between an adapter port and multiple I/O device ports by routing
connections between the expander ports. Only a single connection through an expander can exist at a
time. Using expanders creates more nodes in the path from the adapter to the I/O device. If an I/O
device supports multiple ports, more than one path to the device can exist when there are expander
devices included in the path.
1
© Copyright IBM Corp. 2014, 2017