Introduction - HP e3000 MPE/iX Manual

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Introduction

This manual documents the High Availability FailOver/iX (or HAFO) utilities
for HP e3000 systems running MPE/iX 7.0 and 7.5. HAFO provides protection
from disk I/O path failures to the system and user volume sets by allowing a
System Administrator to configure a "Primary Path" for normal I/O and an
"Alternate Path" for temporary use during the recovery of a primary path failure.
HAFO is also to be used only with multi-ported disk storage array products.
It is critical to understand that HAFO "protection" is available only on a
device's primary path. When running on the alternate path a system is
vulnerable to all the 'normal' I/O failure modes (see Chapter 2, Product
Description). As offered, there is no "automatic" switching from the alternate
path to a "repaired" primary path. However, Command Interpreter scripts can be
written by a System Administrator to implement this functionality.
HAFO does not actively monitor the status of the alternate paths. It is possible
to have a silent failure on an alternate path – this could result in the inability to
complete a failover to the alternate path. Therefore, we strongly recommend that
all HBAs participating in the HAFO configuration have at least one primary
path assigned.
Some modern sports cars have "run flat" tires that allow one to loose air
HAFO Analogy
pressure in a tire and still drive your car, at limited speeds, for a limited distance.
This allows you to drive to the tire store for a repair rather than crashing your
car or requiring a long wait for a tow truck. However, you must decide how to
repair the tire and when it is safe to drive again.
Similarly, HAFO/iX provides the alternate path as a "run flat" option for your
disk Ldev's primary path. The "mileage" limit is subject to your anticipated I/O
path failure rate, the longer you run on the alternate path the more likely you are
to experience an actual system interruption. Your "speed" limit depends on your
alternate path hardware configuration. The "switch" onto the alternate path is
automatic. The decision to switch back to the repaired primary path is manual.
Luckily, unlike the repair of a tire, the switch back to the primary path can, in
many cases, be accomplished without stopping your system.
Introduction
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