IBM SAS RAID controllers, Руководство пользователя

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physical links. A port is a wide port if there are more than one physical link in the 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).
An 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 Advanced Technology Attachment (ATA) and Advanced
technology Attachment Packet Interface (ATAPI) command set depending on the device type.
An 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 given time. Using expanders creates more nodes in the path from the controller 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.
An SAS fabric refers to the summation of all paths between all SAS controller ports and all I/O device
ports in the SAS subsystem including cables, enclosures, and expanders.
The following example SAS subsystem shows some of the concepts described in this SAS overview. A
controller is shown with eight SAS physical links. Four of those physical links are connected into two
different wide ports. One connector contains four physical links grouped into two ports. The connectors
have no significance in SAS other than causing a physical wire connection. The four-physical links
connector can contain one to four ports depending on the type of cabling that is used. The uppermost
port in the figure shows a controller-wide port number 6 that consists of physical link numbers 6 and 7.
Port 6 connects to an expander, which attaches to one of the dual ports of the I/O devices. The dashed
red line indicates a path between the controller and an I/O device. Another path runs from the
controller's port number 4 to the other port of the I/O device. These two paths provide two different
connections for increased reliability by using redundant controller ports, expanders, and I/O device ports.
The SCSI Enclosure Services (SES) is a component of each expander.
Disk arrays
Disk arrays are groups of disks that work together with a specialized array controller to take advantage of
potentially higher data transfer rates and data redundancy.
Figure 19. Example SAS subsystem
SAS RAID controllers for IBM i
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