Chapter 2. Architecture and technical overview
75
a PCIe slot in a system enclosure. This adapter controls the third set of bays. By having three
controllers, you can have three sets of boot drives supporting three partitions.
You can configure the two embedded controllers together as a pair for higher redundancy or
you can configure them separately. If you configure them separately, they can be owned by
separate partitions or they can be treated independently within the same partition. If
configured as a pair, they provide controller redundancy and can automatically switch over to
the other controller if one has problems. Also, if configured as a pair, both can be active at the
same time (active/active) assuming that two or more arrays are configured, providing
additional performance capability and also redundancy. The pair controls all six small form
factor (SFF) bays and both see all six drives. The dual split (3/3) and triple split (2/2/2)
configurations are not used with the paired controllers. RAID 0 and RAID 10 are supported,
and you can also mirror two sets of controller or drives using the operating system.
Adding the optional 175 MB Cache RAID - Dual IOA Enablement Card (FC 5662) causes the
pair of embedded controllers to be configured as dual controllers, accessing all six SAS drive
bays. With this feature, you can get controller redundancy, additional RAID protection options,
and additional I/O performance. RAID 5 (a minimum of three drives is required) and RAID 6 (a
minimum of four drives is required) are available when configured as dual controllers with one
set of six bays. The Dual IOA Enablement Card (FC 5662) plugs in to the disk or media
backplane and enables a 175 MB write cache on each of the two embedded RAID adapters
by providing two rechargeable batteries with associated charger circuitry.
The write cache can provide additional I/O performance for attached disk or solid-state drives,
particularly for RAID 5 and RAID 6. The write-cache contents are mirrored for redundancy
between the two RAID adapters, resulting in an effective write cache size of 175 MB. The
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 a 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 5887)
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 30
SAS bays (six SFF bays in the system unit and 24 SFF 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 30-bay configuration, all drives must be
HDDs. An FC 5886 SAS disk drawer can similarly be configured in place of the FC 5887
drawer.
IBM i supports configurations that use one set of six bays but does not support logically
splitting the backplane into dual or triple split. Thus, the Dual IOA Enablement card (FC 5662)
Rules: The following SSD or HDD configuration rules apply:
You can mix SSD and HDD drives when configured as one set of six bays.
If you want to have both SSDs and HDDs within a dual split configuration, you must use
the same type of drive within each set of three. You cannot mix SSDs and HDDs within
a subset of three bays.
If you want to have both SSDs and HDDs within a triple split configuration, you must
use the same type of drive within each set of two. You cannot mix SSDs and HDDs
within a subset of two bays. The FC 5901 PCIe SAS adapter that controls the remaining
two bays in a triple split configuration does not support SSDs.
