IBM Power 780 Technical Overview And Introduction page 94

batteries provide power to maintain both copies of write-cache information in the event that
power is lost.
Without the Dual IOA Enablement Card, each controller can access only two or three SAS
drive bays.
Another expansion option is an SAS expansion port (FC 1819). The SAS expansion port can
add more SAS bays to the six bays in the system unit. A DASD expansion drawer (FC 5886)
is attached using a SAS port on the rear of the processor drawer, and its two SAS bays are
run by the pair of embedded controllers. The pair of embedded controllers is now running 18
SAS bays (six SFF bays in the system unit and twelve 3.5-inch bays in the drawer). The disk
drawer is attached to the SAS port with a SAS YI cable, and the embedded controllers are
connected to the port using a FC 1819 cable assembly. In this 18-bay configuration, all drives
must be HDDs.
IBM i supports configurations that use one set of six bays but does not support logically
splitting the backplane into split (dual or triple). Thus, the Dual IOA Enablement card
(FC 5662) is required if IBM i is to access any of the SAS bays in that CEC enclosure. AIX
and Linux support configurations using two sets of three bays (3/3) or three sets of two bays
(2/2/2) without the dual IOA enablement card. With FC 5662, they support dual controllers
running one set of six bays.
Figure 2-19 shows the internal SAS topology overview.
Integrated
SAS Adapter
P7IOC
P7IOC
Redriver
External Port
Figure 2-19 Internal SAS topology overview
The system backplane also includes a third embedded controller for running the DVD-RAM
drive in the CEC enclosure. Because the controller is independent from the two other SAS
disk or SSD controllers, it allows the DVD to be switched between multiple partitions without
affecting the assignment of disks or SSDs in the CEC drawer.
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IBM Power 770 and 780 (9117-MMD, 9179-MHD) Technical Overview and Introduction
Redriver
Integrated SAS Port Exp.
SAS Adapter
Optional
Battery
Optional
Battery
Integrated SAS Port Exp.
SAS Adapter
VSES
DVD
A
DASD
DASD
B
DASD