IBM Power 780 Technical Overview And Introduction page 93

Power 770 and Power 780 supports various internal storage configurations:
Dual split backplane mode: The backplane is configured as two sets of three bays (3/3).
Triple split backplane mode: The backplane is configured as three sets of two bays (2/2/2).
Dual storage IOA configuration using internal disk drives (Dual RAID of internal drives
only): The backplane is configured as one set of six bays.
Dual storage IOA configuration using internal disk drives and external enclosure (Dual
RAID of internal drives and external drives).
Configuration options can vary depending on the controller options and the operating system
that is selected. The controllers for the dual split backplane configurations are always the two
embedded controllers. But if the triple split backplane configuration is used, the two integrated
SAS controllers run the first two sets of bays and require a SAS Controller adapter (FC 5901)
located in a PCIe slot in a CEC enclosure. This adapter controls the third set of bays. By
having three controllers, you can have three boot drives supporting three partitions.
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.
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/drives using the operating system.
Power 770 and Power 780, with more than one CEC enclosure, support enclosures with
different internal storage configurations.
Adding the optional 175 MB Cache RAID - Dual IOA Enablement Card (FC 5662) causes the
pair of embedded controllers in that CEC drawer 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. 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
Chapter 2. Architecture and technical overview
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