IBM 8231-E2B Manual page 17

HA single system configuration
An HA single system configuration provides for redundant adapters from a single system to the same set
of disks and disk arrays. This feature is typically referred to as Multi-Path I/O (MPIO). MPIO support is
part of the operating system support and can be used to provide a redundant IBM SAS RAID controller
configuration with RAID protected disks.
Auxiliary write cache adapter
The auxiliary write cache (AWC) adapter provides a duplicate, nonvolatile copy of write cache data of the
RAID controller to which it is connected.
Protection of data is enhanced by having two battery-backed (nonvolatile) copies of write cache, each
stored on separate adapters. If a failure occurs to the write cache portion of the RAID controller, or the
RAID controller itself fails in such a way that the write cache data is not recoverable, the AWC adapter
provides a backup copy of the write cache data to prevent data loss during the recovery of the failed
RAID controller. The cache data is recovered to the new replacement RAID controller and then written
out to disk before resuming normal operations.
The AWC adapter is not a failover device that can keep the system operational by continuing disk
operations when the attached RAID controller fails. The system cannot use the auxiliary copy of the
cache for runtime operations even if only the cache on the RAID controller fails. The AWC adapter does
not support any other device attachment and performs no other tasks than communicating with the
attached RAID controller to receive backup write cache data. The purpose of the AWC adapter is to
minimize the length of an unplanned outage, due to a failure of a RAID controller, by preventing loss of
critical data that might have otherwise required a system reload.
It is important to understand the difference between multi-initiator connections and AWC connections.
Connecting controllers in a multi-initiator environment refers to multiple RAID controllers connected to a
common set of disk enclosures and disks. The AWC controller is not connected to the disks, and it does
not perform device media accesses.
The RAID controller and the AWC adapter each require a PCI bus connection and are required to be in
the same partition. The two adapters are connected by an internal connection. For the planar RAID
enablement and planar auxiliary cache features, the dedicated connection is integrated into the system
planar.
Related tasks:
Serial-attached SCSI cable planning
Learn about how to install the SAS cables to the hard disk drives or solid-state drives.
Related reference:
"PCIe RAID and SSD SAS adapter 3 Gb (FC 2053, FC 2055; CCIN 57CD)" on page 167
Learn about the specifications and operating system requirements for the feature code (FC) 2053 or 2055
adapter.
"PCIe Dual - x4 3 Gb SAS RAID Adapter (FC 5903 and FC 5805; CCIN 574E)" on page 174
Learn about the specifications and operating system requirements for the feature code (FC) 5903 and FC
5805 adapters.
"PCIe2 1.8 GB Cache RAID SAS Tri-port 6 Gb Adapter (FC 5913; CCIN 57B5)" on page 180
Learn about the specifications and operating system requirements for the feature code (FC) 5913 adapters.
"PCIe2 RAID SAS Adapter Dual-port 6Gb (FC ESA1; CCIN 57C4)" on page 184
Learn about the specifications and operating system requirements for the feature code (FC) ESA1
adapters.
"PCIe2 RAID SAS Adapter Dual-port 6-Gb LP (FC ESA2; CCIN 57C4)" on page 186
Learn about the specifications and operating system requirements for the feature code (FC) ESA2
5
Managing PCI adapters