Cache-A is an older format so the tapes are typically old and inherit risk of tape issues.
Due to the nature that cache- a is a unique format, there are certain conditions where certain files are unreadable.
Data may error due to age of the tapes degrading over time.
1. If an individual file or selected files tend to fail to restore then the best workflow is to try to restore the entire tape. If the TOC analysis finds missing files or if the Tar Header fails to read for example, it is best to restore the entire tape.
2. If the restore continues to fail, then a recovery would then need to be run in attempts to pull as much data from the tape as possible.
3. If tape continues to fail and the drive is in good working health, then the tape will need to be sent into a data recovery facility. Please see article here regarding data recovery.
Restoring Cache-A Spanned tapes
When restoring a Cache-A span, you will need to insert the Last Tape in the Span for the system to read the TOC from that tape to then find the file(s) from the various tapes. The restore workflow applies here as well if file(s) are not able to be restored.