Hi, i think i'll close this off. We went with Acronis Echo but still not entirely happy with the solution. The reason being is they truly need real-time backup to a device or other machine.
With any imaging software there is always going to be at least 5 minutes delay and the average robbery is less than 3 minutes. That's not enough time to ensure the video that is backed up actually contains footage of the robbery and any subsequent destruction of the machine would result in total loss of security footage.
In regards to QuinTain's comments, the machine is hidden somewhere obscure in the hotel so this really is a worst case scenario backup.
Thanks all for helping.