Just to clarify the title, I'm not looking for a backup product, mostly because I don't think it will do what I need.
The problem:
Every night, around 1AM each front-end server backups every single file associated with a site, which include images, configuration files, data files, log files, etc. Each server on average has between 2-3 million files to be copied every night.
Currently, I wrote my own backup solution which checks file timestamp and syncs two folders on separate disks.
For example, for "marcelo.sampasite.com" there is the site folder on drive C and a backup folder on drive D. Every night, the C folder will synchronize with D folder. The key here is that it doesn't take the site offline so every file copy locks the site for a few miliseconds.
What I need?
My stupid file-sync algorithm is becoming too slow. It takes many hours to sync each server hard disk. I need something that is faster, optimized for Windows, and, ideally, would be able to integrate into my app so that it can copy files while we have open handles to it.
I'm looking at calling Robocopy, but I'm not sure that is optimum. I'm also wondering if Windows Shadow Copy can help with that. Anyone has experience doing this?
I'm the Co-founder & CTO of 
