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240 EMC Symmetrix DMX-3 Product Guide
Mainframe Features and Support
Error reporting and recovery
This section discusses the types of errors possible when the
Symmetrix system is connected to a mainframe host. It also discusses
error handling techniques and an error recovery summary.
Types of errors
There are several types of errors associated with data storage. The
error type is indicated in the sense information, and in error messages
and reports. You should be aware, however, that the error type
doesn't necessarily identify the source or the cause of the problem.
The error types detected by the Symmetrix system include the
following:
◆
Data Check — The Symmetrix system has detected an error in the
bit pattern read from the disk. Data checks are due to hardware
problems when writing or reading data, media defects, or
random events.
◆
System or Program Check — The Symmetrix system has rejected
the command. This condition is attributed to the construction of
the channel program. This type of error is indicated to the
processor and is always returned to the requesting program.
◆
Overrun — The Symmetrix system cannot receive data at the rate
it is transmitted from the host system. This error indicates a
timing problem. Resubmitting the I/O operation usually corrects
this error.
◆
Equipment Check — The Symmetrix system has detected an error
in hardware operation.
Temporary and
permanent errors
Whenever the Symmetrix system detects a data or equipment error,
either the Symmetrix system or the host operating system will
attempt to recover from the error, depending on the situation and the
type of hardware involved. Error recovery can be temporary or
permanent.
An error is temporary if the Symmetrix system or the host operating
system can recover from the error successfully. The application is not
notified of a temporary error. Temporary errors recovered within the
Symmetrix system are not listed in the error report unless its internal
soft error threshold has been exceeded. Temporary errors recovered
by the operating system are logged by the host Error Recovery
Procedures (ERP). When requested, the Symmetrix system generates
sense bytes and sends them to the operating system. These sense
bytes define the error.