I'm looking for SW utility (for Windows 7 x64) which is able to run as background process, monitor selected folders and synchronize changes to backup folder on different drive (incremental backup). It would be nice if background process execute synchronization only if disk drives are not under heavy load. Utility must be lightweight - no big SW package with millions of settings which consumes a lot of processing power.
I understand that under some circumstances folders don't have to be fully synced because of asynchronnous behavior but it is what I want.
I know that this would be much easier done with mirrored disks (RAID) but I want to backup only few folders, not whole content of the disk. The intention is to backup Windows user profiles so if the system has to be restored from backup (or if disk crashes) user data are not lost.
The SW can be commercial - I'm ready to buy it but it should not be too expensive - generally has to be less expensive then second disk to RAID array. I'm not looking for custom solution - I can probably build it myself but I would like to have something that already proved its quality.