Backup file has not changed in size
KB006 – Explanation of backup snap-shots on Firebird database software
This document is only applicable to systems where the Firebird database software is used on the server.
Backup files are a snap-shot of the complete database and usually have the extension NBK.
When the database grows, it takes more disk space than it actually requires.
This additional space is filled until more space is required.
At this point the database will increase in size, taking up more space. This cycle is repeated.