Archive Logs

IBM MQ archive logs on z/OS are the long-term memory of everything the active logs already saw. Active logs are small, fast, and cyclic—meant to receive today’s firehose of persistent puts. When an active log data set fills, the archiving process copies its records to an archive log data set, registers that data set in the BSDS with starting and ending relative byte addresses, and frees the active log to accept new records. Without archiving, active logs would hit capacity in hours and the queue manager would halt durable messaging. Without retaining archives long enough, disaster recovery cannot roll page sets forward from last night’s backup to this morning’s failure point. Beginners should treat archive management as equal to channel tuning—not optional housekeeping. This tutorial explains the archive cycle, naming and cataloging in BSDS, retention and tape migration, forward recovery role, operational failure modes, and coordination with checkpoints and page set backups.

The Archive Cycle

1. Active log Log 1 or Log 2 receives continuous log records.
2. Active log reaches size or policy threshold.
3. Archiving utility copies records to a new archive log data set.
4. BSDS updated with archive data set name and RBA range.
5. Active log space reclaimed for new records.
6. Archive retained per policy—DASD, tape, or virtual tape.

BSDS Registration

Each archive data set appears in BSDS with identifiers operators use during recovery. Missing registration—archive exists on tape but BSDS never updated—causes recovery to stop at a gap. Operations verify archive jobs end RC=0 and BSDS entries appear before declaring success. Duplicate or overlapping archive names from manual mistakes require IBM cleanup procedures.

Retention and Tape Management

Retention policy answers: how far back can we restore page sets? If page set backup is daily at 02:00 and you need recovery to 14:00, you need archive logs covering that interval. Many sites migrate archives to tape with HSM or batch jobs, keeping recent archives on DASD for speed. Legal hold and audit may require longer retention than operations prefers—governance wins over disk cost.

• Define recovery point objective (RPO) in business terms.
• Map RPO to minimum archive retention on disk and tape.
• Automate catalog of tape volumes with queue manager name and date.
• Test restore from tape yearly—tapes degrade and procedures drift.

Forward Recovery with Archives

Media recovery restores page sets from backup taken at time T0, then replays archive logs from T0 forward through log records until desired time T1. Checkpoints on restored page sets may not match backup age—recovery utilities apply logs in order. Operators document T1 carefully for regulatory “restore to 10:03 before bad deployment” requests.

1
2
3
4
5
6
/* Conceptual media recovery sequence
   1. Restore page sets from backup (T0)
   2. Restore BSDS consistent with backup or use recovery utility
   3. Identify archive logs covering T0 to T1 from BSDS
   4. Replay archive and active logs per IBM procedure
   5. Start queue manager; verify queue depths */

Operational Failure Modes

Archiving and Performance

Archiving consumes I/O and CPU while applications run. Schedule heavy maintenance windows when possible. Sudden persistent traffic spikes fill active logs faster, increasing archive frequency—capacity planning links message rate to log and archive DASD. Monitor CSQ messages referencing log and archive status during month-end batch.

Coordination with Checkpoints

Checkpoints reduce restart replay from active logs; archives extend the timeline for major recovery. Together they form the z/OS MQ durability story with page sets and BSDS. Read the logs, BSDS, page sets, and checkpoints tutorials as one module.

Explainer: Moving Diaries to the Attic

Active logs are the desk diary you write in daily. Archive logs are bound volumes moved to the attic when the desk is full. BSDS is the card catalog listing which attic box holds which dates.

Explain Like I'm Five

When one diary notebook is full, MQ copies it to a big storage box and starts a fresh notebook. It keeps a list of every storage box so it can find old pages later.

Practice Exercises

Exercise 1

Given daily page set backup at 02:00 and failure at 15:30, list archives needed for forward recovery.

Exercise 2

Write retention policy bullets for 7-day DASD and 90-day tape archives.

Exercise 3

Diagram archive cycle with Log 1, Log 2, and BSDS update.

Frequently Asked Questions

Test Your Knowledge