Real-time offline folder-to-folder backup application needed (Windows)

I do not think you can write something that is going to be sufficiently fast enough to keep you happy, while consuming very little CPU and resources. The task of compression into rar, zip, or 7z format is CPU intensive, and disk intensive.

I suspect that a "nearly realtime" system that can almost keep up with your working rates would have to be very intelligent indeed.

If you can not live with an overnight full backup of your Raid0 system, then you shouldn't be using Raid0 at all, in my opinion. I used this exact configuration for my primary system for several years and found no noticeable performance benefit in Raid0 when I did it with a bunch of commodity 7200 rpm drives. Instead, I decided to go with a single Velociraptor drive, and a second drive to back it up to. Lower MTBF risk, and higher performance for the same dollars, and in my opinion, no need for instant realtime backup.

In effect, IF you are trying to turn your Raid0 into something as "safe as Raid5" without losing the benefit of Raid0's speed compared to Raid5. I do not believe it can be done. In fact, I could almost guarantee that Raid5 in-hardware compared to backup-in-software will result in a net loss of usable disk bandwidth that will make your complex system both more likely to fail, and lower performance, than a single Velociraptor drive running unencumbered by realtime backup or RAID.

I didn't see a mention of OS. If you are running Windows, have you looked at RoboCopy? It is free. It can be setup as a Windows Service (using SrvAny), and (after the intial mirror) runs fast and uses very few resources.

I have used it to mirror a few folder structures from one server to the other where it was running as a service. I didn't have super stringent requirements for real-time in that instance; but I believe you can either have it run continuously, or on a very tight schedule.

Might be worth a look...