In Simple DNS Plus v. 6.0 and later, the DNS zones and records, and the different program settings (Options dialog etc.) are all stored in a single database file called "sdnsplus.db" in the Simple DNS Plus application data directory.
On Windows Vista / Server 2008 and later, this location is typically:
C:\ProgramData\JH Software\Simple DNS Plus
On earlier Windows versions:
C:\Documents and Settings\All Users\Application Data\JH Software\Simple DNS Plus
You can shut down Simple DNS Plus, make a copy of that file, and that's your backup.
However, as it is likely not very convenient to shut down your DNS server at any schedule, Simple DNS Plus includes a command line option (-b) to make a copy of the database (at a safe point) while the program is still live and running.
sdnsplus.exe -b "c:\my backups\sdnsplus.db"
To later restore this on a new or reinstalled computer, simply install a fresh copy of Simple DNS Plus, and copy the backup file to the Simple DNS Plus application data directory as "sdnsplus.db".
Scheduling daily backups
You can of course also use above command line option as part of a backup script, or with Windows scheduler.
For example, to schedule a backup every night at 3:00 AM (on recent Windows versions), right-click the Windows Start button and select "Computer Management":
Right-click "Task Scheduler" and select "Create Task...":
Enter a name for the task, and select "Run whether user is logged on or not":
Select the "Triggers" tab and click the "New..." button:
Select "Daily" and enter "3:00:00 AM" and click the "OK" button:
Select the "Actions" tab and click the "New button":
In the "Program/script" field enter the path to sdnsplus.exe and in the "Add arguments" field enter "-b", space, and the path to the backup file (remember quotes if it contains spaces), and click the "OK" button:
Back in the "Create Task" window, click the "OK" button:
Enter your password, and the daily backup task has been scheduled:
Finally make sure to point your backup software to this backup folder.