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14 Chapter 2
Subsystem Architecture and Components
2.2 Components of the Controller Frame
The 9900 controller frame contains the control and operational components of the
subsystem. For the 9910 subsystem, the controller frame also contains the disk array
components. The 9900 controller is fully redundant and has no active single point of failure.
All controller frame components can be repaired or replaced without interrupting access to
user data. The key features and components of the controller frame are:
Storage clusters (see section 2.2.1),
Nonvolatile duplex shared memory (see section 2.2.2),
Nonvolatile duplex cache memory (see section 2.2.3),
Multiple data and control paths (see section 2.2.4),
Redundant power supplies (see section 2.2.5),
CHIPs and channels (FICON™, ExSA™, and/or fibre-channel) (see section 2.2.6),
ACPs (see section 2.2.8).
2.2.1 Storage Clusters
Each controller frame consists of two redundant controller halves called storage clusters.
Each storage cluster contains all physical and logical elements (e.g., power supplies, CHAs,
CHIPs, ACPs, cache, control storage) needed to sustain processing within the subsystem.
Both storage clusters should be connected to each host using an alternate path scheme, so
that if one storage cluster fails, the other storage cluster can continue processing for the
entire subsystem.
Each pair of channel adapters is split between clusters to provide full backup for both front-
end and back-end microprocessors. Each storage cluster also contains a separate, duplicate
copy of cache and shared memory contents. In addition to the high-level redundancy that
this type of storage clustering provides, many of the individual components within each
storage cluster contain redundant circuits, paths, and/or processors to allow the storage
cluster to remain operational even with multiple component failures. Each storage cluster is
powered by its own set of power supplies, which can provide power for the entire subsystem
in the unlikely event of power supply failure. Because of this redundancy, the Lightning
9900™ subsystem can sustain the loss of multiple power supplies and still continue operation.
Note: The redundancy and backup features of the Lightning 9900™ subsystem eliminate all
active single points of failure, no matter how unlikely, to provide an additional level of
reliability and data availability.