Log errors

You can experience three types of errors during logging. A write error on the OLDS, a read error on the OLDS or SLDS, and a read or write error on the WADS can occur.

OLDS write error

When an OLDS has a write error, IMS stops the OLDS (or a pair of OLDSs) in error. No specific MTO interaction is required. When an OLDS is no longer needed for dynamic backout, IMS dynamically deallocates a stopped OLDS.

If you are using single logging, IMS switches to the next OLDS. If the error causes only two OLDSs to remain available, IMS terminates. If an error occurs and no other OLDS is available, IMS abends with code U0616.

If you are using dual logging and an error occurs (either to one or both volumes in the pair), IMS switches to the next OLDS pair and continues. What happens next depends on what is specified on the DEGRADE control statement of the LOGGER section of the DFSDFxxx member.

DEGRADE=YES

Specifies that IMS will continue to use all good pairs of OLDSs until only two pairs remain. At this point, IMS switches (degrades) to single-logging mode, using whatever good data sets are left from each pair of OLDSs. When only two good OLDSs remain, IMS terminates (as it does in normal single-logging mode). DEGRADE=YES is the default.

DEGRADE=NO

Specifies that IMS will terminate when only two good pair of OLDSs remain.

Recommendation: Use the /START OLDS command to allocate new pairs of OLDSs.

OLDS or SLDS read error

When read errors occur on the OLDS or the SLDS during emergency restart, IMS abends. When read errors occur on the OLDS during dynamic backout, backout fails.

WADS error

When a WADS has an I/O error, IMS switches to another WADS if one is available. If none is available, processing continues without a WADS. IMS maintains log-write-ahead protocols by truncating log buffers. As with OLDS errors, no specific MTO interaction is required. You should scratch and reallocate any WADS with a write error after you shut down IMS.