Availability Guide for Application Design

Glossary
Availability Guide for Application Design—525637-004
Glossary-17
operations outage class
operations outage class. An outage class that includes errors caused by operations
personnel due to accidents, inexperience, or other actions.
operator message. The text displayed for a system operator that describes an event.
OSS. See Open System Services (OSS).
OSS environment. The Open System Services (OSS) API, tools, and utilities.
outage. Time during which the NonStop system is not capable of doing useful work because
of a planned or unplanned outage. From the end-user’s perspective, an outage is any
time the application is not available.
outage class. A concept developed by HP to categorize the causes of outages. There are
five outage classes: physical, design, operations, environmental, and reconfiguration.
The first four categories describe unplanned outages. The reconfiguration outage class
includes all planned outages.
outage log. A record of system outages. An outage log can provide an accurate
assessment of availability. HP recommends that outages be measured in minutes
rather than percentages. See also outage minutes.
outage minutes. A metric recommended by HP for measuring outages that translates
percentages into minutes of downtime per year.
parity check. Testing a group of bits to determine whether the number of ones in the group
is odd or even.
passive backup. A programming technique used to achieve fault tolerance in application
programs. In passive backup programming, a process executes as a process pair: a
primary process, which performs the application processing, and a backup process,
which is ready to take over execution if the primary process fails. The backup process
of a passive backup process pair is updated when the primary process checkpoints
information; the updated information is physically the same as in the primary.
Contrast with active backup.
PATHCOM. The command-language interpreter used to communicate interactively with
PATHMON to configure and control Pathway.
PATHMON process. The central control process for a PATHMON system. PATHMON
controls all processes and devices in the Pathway environment and provides the
means to configure, manage, monitor, and change the PATHMON configuration.
Pathsend procedures. The set of Guardian procedure calls that provide general access to
Pathway server classes from any process on a HP system. See also Link manager
process.
Pathsend process. A process, written as a Guardian program in C, C++, COBOL85,
Pascal, or TAL, that makes calls to Pathsend procedures to request services from a