Complications in recovery

If you could always recover a system simply by knowing where you started and keeping track of what you have done since then, it would be easy. Unfortunately, complications often arise, not only in the data and applications, but in the mechanisms of recovery themselves.

The IMS logs (on DASD or tape) are just as subject to I/O problems as any other data set. You can run out of space, or develop physical problems with the drive. The internal IMS modules involved in recovery are totally dependent on the operating system and hardware; if the system crashes for any reason (for example, power failure, abend, hardware malfunction), the recovery processing performed by these modules might be incomplete.

So, recovering from a problem can be a two-part process: first you must recover the IMS recovery tools themselves, then you can recover the data and applications.