COMPAKTOR Error Recovery

COMPAKTOR is designed to handle various error conditions by recovering from the errors. Recovery actions are as follows:

VTOC errors

COMPAKTOR recovers from certain VTOC error conditions, such as invalid F5 DSCBs and invalid flags in extent descriptors, automatically.

I/O errors

I/O errors while reading/writing a VTOC or the first few blocks of an FDR dump tape (the DSF blocks) cause immediate abnormal termination. This is because the involved volumes are essentially unusable.

DASD I/O errors

When operating system error recovery notifies COMPAKTOR of a permanent I/O error while writing a DASD track during the restore, COMPAKTOR skips that track. Up to 20 tracks in error may be skipped. At the end of the restore operation, COMPAKTOR prints a list of all non-restored, or skipped tracks; the data sets involved can be determined by comparing this list to the BEFORE map. It is then up to you to determine whether the restored volume is usable or not.

A FASTCPK terminates when even one DASD I/O error occurs. If the error is in the early stages of FASTCPK, no harm has been done and the COMPAKTion simply terminates. If changes have been made in the volume, COMPAKTOR automatically enters recovery (see FASTCPK Recovery) and returns the volume to its original state.

Tape I/O errors

When COMPAKTion-from-backup is notified of a permanent I/O error while reading from the backup data set by system error recovery, it skips the bad tape blocks and attempts to restore as much of the volume as possible. Each tape block may contain one or more original DASD tracks. A list of non-restored tracks is printed after the end of the restore operation; the data sets involved can be determined by comparing this list to the BEFORE map. It is then up to you to determine whether the restored volume is usable or not. Up to 20 tape blocks may be skipped.

Usable volumes

When mapping or simulating, all volumes are always usable, since COMPAKTOR never alters them.

When compacting, a volume is usable if:

• Message CPK321I was not issued prior to termination.
• If message CPK322I was issued prior to termination. However, if termination was abnormal, the volume may or may not be usable.

If LOG=YES was specified, CPK also issues message FDRW82 to the operator concurrent with the CPK321I and CPK322I messages, so that the operator knows when CPK has begun modifying the volume and when it is done.

I/O Error diagnostics

When a tape or DASD I/O error is encountered, COMPAKTOR prints a diagnostic DUMP to aid you and us in identifying the track or block in error and the cause of the error.

FASTCPK recovery

Fast COMPAKTion (FASTCPK) maintains a log on the DASD volume in which all track movement is recorded. If any error condition prevents FASTCPK from completing, it automatically enters a recovery routine that moves every track back to its original location, returning the volume to its original state.

If the FASTCPK job is prematurely terminated with no opportunity to recover (such as a system crash), another FASTCPK job run against the volume recognizes that this occurred and uses the recovery log to perform the same recovery, automatically. A CPK MAP job notifies you that the recovery is pending.