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Appendix G High Availability
536 September 2002 HPSS Installation Guide
Release 4.5, Revision 2
High availability is not the same as fault tolerance. The failures above are “protected against” from
the standpoint that the HA HPSS system will be able to return to an operational state without
intervention when any one of the above failures occur. There certainly may be some down-time,
especially when the core server fails (crashes).
After a recovery, HPSS will function properly, but it will no longer be in a Highly Available state. A
subsequent failure may not be recoverable. For instance, if the core server crashes and the backup
takes over, there is no longer a backup node. It will be necessary to correct the original failure in
order to return the system to a Highly Available state.
G.1.1 Architecture
The following diagram shows the necessary components for an HA HPSS configuration:
Figure H-1 HA HPSS Architecture
This diagram does not include the power system, but it does have several features that are very
important:
• At any point in time, either Node 1 or Node 2 can act as the core HPSS server.
• The two shared disk busses are mirrored to one another and accessed by each node using
separate adapter cards so that any single failure (disk, adapter, or bus) will result in
accessibility of at least one good copy of the data.
Node 1 Node 2
Disks
Disks
RS-232 Network
Clients Movers
Ethernet
Network