Читаем в документации https://www.ibm.com/support/knowled...admin85.doc/H_COMPACT_OPTIONS_1761_STEPS.html
Вопрос - зачем делать бекап после компакта? почему не перед компактом, что выглядит логичнее?In-place with file size reduction
-B
Uses in-place compacting, recovers unused space and reduces file size, unless there's a pending structural change in which case copy-style compacting occurs. If you use transaction logging, do full database backups after compacting completes.