Firebird stores and maintains all of the metadata for its own and your user-defined objects in – a Firebird database! More precisely, it stores them in relations (tables) right in the database itself. The identifiers for the system tables, their columns and several other types of system objects begin with the characters RDB$.

Because these are ordinary database objects, they can be queried and manipulated just like your user-defined objects. However, just because you can does not say you should. The Firebird engine implements a high-level subset of SQL (DDL) for the purpose of defining and operating on metadata objects, typically through CREATE, ALTER and DROP statements.

It cannot be recommended too strongly that you use DDL – not direct SQL operations on the system tables – whenever you need to alter or remove metadata. Defer the “hot fix” stuff until your skills in SQL and your knowledge of the Firebird engine become very advanced. A wrecked database is neither pretty to behold nor cheap to repair.

Firebird is installed with forced writes (synchronous writes) enabled by default. Changed and new data are written to disk immediately upon posting.

It is possible to configure a database to use asynchronous data writes – whereby modified or new data are held in the memory cache for periodic flushing to disk by the operating system's I/O subsystem. The common term for this configuration is forced writes off (or disabled). It is sometimes resorted to in order to improve performance during large batch operations.

The big warning here is: do not disable forced writes on a Windows server. It has been observed that the Windows server platforms do not flush the write cache until the Firebird service is shut down. Apart from power interruptions, there is just too much that can go wrong on a Windows server. If it should hang, the I/O system goes out of reach and your users' work will be lost in the process of rebooting.

One of the restore options in the gbak utility (gbak -r[eplace]) allows you to restore a gbak file over the top of an existing database. It is possible for this style of restore to proceed without warning while users are logged in to the database. Database corruption is almost certain to be the result.

If is practicable to do so, it is recommended to restore to spare disk space using the gbak -c[reate] option and test the restored database using isql or your preferred admin tool. If the restored database is good, shut down the server. Make a filesystem copy of the old database and then copy the restored database file (or files) over their existing counterparts.

If you do not block access to users while performing a restore using gbak -r[eplace] then users may be able to log in and attempt to do operations on data. Corrupted structures will result.