I am looking for software which will allow me to sync the entire drive (E:) to a folder on another drive (D:). It should be completely free and should copy new files from E: to that folder on D: every 3-6 hours.
I have been using BitITorrent Sync and am very pleased with it.
It is free, easy to set up and handles more devices than just PCs.
Ufortunately, I am behinfd acompany firewall at the moment, so can't access it's home page to quote form there. This is from Wikipedia:
BitTorrent Sync by BitTorrent, Inc is a proprietary peer-to-peer file synchronisation tool available for Windows, Mac, Linux, Android, iOS, Windows Phone, Amazon Kindle Fire and BSD. It can sync files between devices on a local network, or between remote devices over the Internet via a modified version of the BitTorrent protocol.
Although not touted by the developers as an intended direct replacement nor competitor to cloud-based file synchronisation services, it has attained much of its publicity in this potential role.1 This is mainly due to the ability of BitTorrent Sync to address many of the concerns in existing services relating to file storage limits, privacy, cost, and performance.
There is a nice review from PC mag here.