Shunted units of recovery

The following list gives reasons why a unit of recovery might be shunted.

A VSAM RLS cache structure, or connection to it, has failed.
A log stream became or was made unavailable.
A sync point for a unit of recovery failed for one of the data sets that it was using. In this case, the name of the data set and the reason for the failure are included. Failure can occur for any of these reasons:
- The commit failed.
- An error occurred at some point when RLS locks were in the process of being released. This error can normally be resolved by recycling the SMSVSAM server (which should happen automatically).
- The locks were acquired as a result of recoverable requests having been issued against the data set.
- A data set is full; no space is available on the direct access device for adding records to it. You need to reallocate the data set with more space. You can then retry the backout using SHCDS RETRY. You can also find information in
  Various levels of authorization are required to use the SHCDS parameters.
- Backout failed. This occurs as a result of a severe error being identified during backout, and is possibly an error in either DFSMStvs or VSAM. The problem might go away if the backout is retried.
- Index record is full. A larger alternate index record size needs to be defined for the data set.
- A hard I/O error occurred during backout. To correct this error, restore a full backup copy of the data set and perform forward recovery.
- An attempt to acquire a lock during backout of an update to this data set failed because the RLS lock structure was full. You must allocate a larger lock structure in an available coupling facility and rebuild the existing lock structure into it, then use the SHCDS RETRY command to drive the backout retry.
- An error occurred during an open of the data set for backout. A console message notifies you of the reason for the open error. One likely reason could be that the data set was quiesced.

Related reading:

For information on moving and reallocating data sets, see z/OS DFSMSdfp Storage Administration.
http://publib.boulder.ibm.com/infocenter/cicsts/v3r1/index.jsp
For information about the level of authorization required to use the SHCDS parameters, see z/OS DFSMS Access Method Services Commands.