Manual or Continuous backup?

Manually backing up or have it set to automatically backup?

 
Automatic (scheduled) backup is not exactly continuous backup. You can get truly continuous backup with the proper RAID array, and if you can afford enough drives and the raid controller to do it, you will not even suffer a performance cost. If you are running a mission critical service, that might be worth the cost. But for most of us the purpose of a backup is to avoid losing more than the current work session if your drive fails.
 
Problems with scheduled backups are that they may start to run when you want the machine to be doing something else, or that the machine may not be running when you have scheduled the backup, or that the failure will occur before the backup is scheuled to run. Those problems are avoided by doing a manual backup when you are ready to save something important. The problem with manual backup is that you may forget or otherwise avoid doing it often enough to save what you want to save. I personally find it easier to backup manually, than to come up with a scheduled system that will work. But my machine is pretty much under my control, not running programs while I sleep etc.
 
 
 

"fireberd"
I too do manual backups (using Acronis True Image). I also always do a full hard drive backup, I do not use the incremental backup methods.

Same here..., +1. And I actually disconnect the external backup drive and put it away in a nice dry place until I need it again. Then disable all Acronis related services etc. Current projects I still work on are also saved on a USB stick, aside the usual local copy.

The one I have, a Maxtor 1TB USB drive cannot be "powered" off thru the PC.  The only way it will power off is to unplug the "wall wart" power supply.  

I do the backup with Acronis (usually at night) and check the option in Acronis to power off the PC after the backup is completed.  I'll come back to the PC in the morning and the drive is still on but its not spiinng and probably is some power save mode.

What is the best approach to back up a DAW based system? Manually backing up or have it set to automatically backup?

 
With a DAW, manual backup is the best scenario.
Automatic backups means that scheduling services are running in the background (not ideal for performance reasons).

My WHS Server automaticly backups a image of the DAW. I suppose this is done via a service also?

 
Exactly...
On a DAW, I prefer to initiate backups manually.

I think that it would be important to have a intelligent automatic backup system

 
We're looking for maximum audio performance.
Anything running in the background (that's not absolutely necessary) is diminishing performance.
 
IOW, initiate backups manually.