Raid Support - IBM Power 720 Overview

2.8.1 RAID support

There are multiple protection options for HDD/SSD drives in the Power 720 and Power 740
systems, whether they are contained in the SAS SFF bays in the system unit, in a 12X
attached I/O drawer, or drives in disk-only I/O drawers. Although protecting drives is always
recommended, AIX and Linux users can, at their own risk, choose to keep some or all drives
unprotected, and IBM supports these configurations. IBM i configuration rules differ in this
regard, and IBM supports IBM i partition configurations only when HDD/SSD drives are
protected.
Drive protection
HDD/SSD drive protection can be provided by AIX, IBM i, and Linux software or by the
HDD/SSD hardware controllers. Mirroring of drives is provided by AIX, IBM i, and Linux
software. In addition, AIX/Linux supports controllers providing RAID 0, 1, 5, 6, or 10. IBM i
integrated storage management already provides striping. IBM i also supports controllers
providing RAID 5 or 6. To further augment HDD/SSD protection, hot spare capability can be
used for protected drives. Specific hot spare prerequisites apply.
An integrated SAS controller offering RAID 0, 1, and 10 support is provided in the Power 720
and Power 740 system unit. It can be optionally augmented by RAID 5 and RAID 6 capability
when storage backplane FC EJ01 is added to the configuration. In addition to these
protection options, mirroring of drives by the operating system is supported. AIX or Linux
supports all of these options. IBM i does not use unprotected disks, and uses embedded
functions instead of RAID 10. IBM i does use the RAID 5 or RAID 6 function of the integrated
controllers.
Table 2-22 lists the RAID support by the backplane.
Table 2-22 RAID configurations for the Power 720 and Power 740
Feature code
5618
5618 and EJ02
EJ01
AIX and Linux can use disk drives formatted with 512-byte blocks when being mirrored by the
operating system. These disk drives must be reformatted to 528-byte sectors when used in
RAID arrays. Although a small percentage of the drive's capacity is lost, additional data
protection such as ECC and bad block detection is gained in this reformatting. For example, a
300 GB disk drive, when reformatted, provides around 283 GB. IBM i always uses drives
formatted to 528 bytes. Solid-state drives (SSDs) are always formatted with 528 byte sectors.
Power 720 and Power 740 support a dual write cache RAID feature that consists of an
auxiliary write cache for the RAID card and the optional RAID enablement.
Split JBOD
backplane
No Yes
Yes Yes
No No
RAID 0, 1, RAID 5 and
and 10 6
Yes No
Yes No
Yes Yes
Chapter 2. Architecture and technical overview
External
SAS Port
No
No
Yes
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