Been trying Super Flexible File Synchronizer for a few days now & I've gone & bought it. It can be totally safe if you choose options correctly.
My Reasons:
Acronis True Image is great for full Image Backups & I still use that but the backup files are in an Acronis Image file which you can mount but its not something you would actively use on a hourly/daily basis really.
I have one main PC (doubles up as HTPC) which we use for 90% of all data usage but also a laptop, smart phone, PS3 etc. which I may use to access Music, Pictures, Movies etc. hence the reason I bought the QNAP TS109. Now even with 100 or even Gigabit ethernet data access is much slower than directly off a PC's hard drive & remember, I mentioned the PC is used for 90% of data access.
Super Flexible File Synchronizer has given me the perfect solution.
Rather than have an external drive attched to my QNAP (via USB or eSATA) which we all know isn't a fast option for either Q-Raid1 or Backup, I have the 1TB Samsung drive in the QNAP and the 2nd 1TB Samsung drive (previously in external housing) mounted in my main PC (in addition to its standard 250GB drive for the OS).
Super Flexible File Synchronizer is now used to ensure the Qmultimedia & Public shares on the QNAP are synced to a QNAP folder on the 1TB drive in the PC.
This means my PC accesses data directly & fast off the internal hard drive while the QNAP is available to the other devices & I have duplicate copies of all important data. I have Super Flexible File Synchronizer set to sync each hour & on PC Shutdown.
As to two way Sync, it can be totally safe as you can set up folders where deleted files are copied to rather than immediately deleted. I use the Recyle Folder on the QNAP for this purpose & periodically review & delete (and as you know the Recycle Bin can only be emptied via password entry into the Admin pages
Great bit of software.
My Share Structure:
Public - Open to everybody
Qmultimedia (contains my Music, Movies, Pictures) - Read Only Access for family, full for me)
Qusb & Qdownload - As standard
Qbackup - Location for storing full Acronis Backup Images with Admin Only Access.
Recycle Bin - Catch all for deleted files, password protected for deletion.
PS. The first time I used Super Flexible File Synchronizer it took nearly a full day to Sync files from my QNAP to the QNAP folder on the PC drive (about 600GB I think) but this is still much faster than the Q-Raid1 option which I was never too confident about especially being a Linux newbie & not confident at inspecting the Q-Raid drive via terminal service.