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What is a single point of failure? z/OS MVS Setting Up a Sysplex SA23-1399-00 |
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A single point of failure is an environment where one failure can result in the simultaneous loss of both the coupling facility list structure for a log stream and the local storage buffer copy of the data on the system making the connection. If you were using local storage buffers to duplex data, this can result in loss of log data. When your configuration contains a single point of failure, you can safeguard your data by duplexing data to staging data sets. A single point of failure can also exist for a duplex-mode structure where one failure can result in the simultaneous loss of both structure instances. The two structure instances in this environment are failure-dependent, meaning a single failure will cause the structure data to be lost, even though it is in two copies of the structure. Since a single point of failure can cause the loss of all the log data in the failure-dependent duplex-mode structure, Logger will continue to safeguard the data by using one of its own duplexing methods. When a configuration is not vulnerable to a single point of failure, it is failure independent. System logger evaluates a connection for a single point of failure
based on the location of the coupling facility and its status of volatile
or non-volatile. The coupling facility can reside in one of the following
configurations:
System logger uses the following rules for determining whether
a log stream connection contains a single point of failure:
If a connection contains a single point of failure and STG_DUPLEX(YES) DUPLEXMODE(COND) has been specified in the log stream definition, system logger will duplex coupling facility log data to staging data sets for that connection. If a coupling facility or CPC failure occurs, system logger can retrieve lost coupling facility log data from the staging data sets for a connection with a single point of failure. |
Copyright IBM Corporation 1990, 2014
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