`nbackup` features - an overview

With nbackup, you can perform two different kinds of tasks:

1. Making and restoring of both full and incremental backups. An incremental backup only contains the mutations since some specific previous backup.

2. Locking the main database file so you can subsequently back it up yourself with copying or backup tools of your own choice. In this mode, nbackup doesn't back up anything; it just creates the conditions under which you can safely make the backup yourself. There's a provision for restoring here, too.

Both modes can operate on an active database, without hindering connected users. The backup created will always reflect the state of the database at the beginning of the operation. Furthermore, only SYSDBA and the database owner (and sometimes OS admins) can make a backup, but every user can restore a backup to a new database. In these respects nbackup doesn't differ from gbak.

Advantages of `nbackup`

Both modes: high speed (as high as hardware and OS will allow), because nbackup doesn't look at the actual data. In backup mode the contents are written more or less blindly to the backup file.
Backup/restore mode: time and disk space savings, because you don't need to make a full backup every time. This can make a huge difference with databases in the gigabyte range.
Lock/unlock mode: total freedom in your choice of backup, copy, and/or compression tools.

Limitations of `nbackup`

nbackup will not sweep and compact your database the way gbak does.
You can't change the database owner with an nbackup backup/restore cycle, like you can with gbak.
nbackup can't make transportable backups, that is: backups you can restore on an incompatible platform or under another server version.
At this moment, nbackup should not be used on multi-file databases.
nbackup can only back up local databases. However, in Firebird 2.5 and above its backup and restore tasks can also be performed remotely through the Services Manager.
Except when the Services Manager is used (in Firebird 2.5+) backing up with nbackup requires direct access to the database file. With gbak this is not the case.