NAS/RAID Synchronization?

[Ironman]

Hi everyone! I am looking for something that "sounds" simple and was wondering if anyone had any recommendations.

I am looking to purchase 2 external Hard Drives/RAIDS that will be stored in 2 separate locations. I am hoping to be able to keep them synchronized, so if I add a File to Drive A it will sync to B on its own. Anyone know of a nice simple solution for this?

[SimonV]

rsync would be the obvious solution. Bittorrent Sync is something new, just found out FreeNAS has a plugin for it:

http://blog.bittorrent.com/2014/02/11/sync-hacks-how-to-set-up-freenas-with-bittorrent-sync-using-a-plugin/

Think I'll be setting that up someday too. I have a microserver running FreeNAS with ZFS mirroring but that doesn't protect me if the house burns down 

Edit: if you're talking external drives then bittorrent sync would also be a perfect solution.

[Fred]

Is this home or business use?  What type of NAS?

Most enterprise NAS devices will have a solution for this (though it may cost extra).  In those cases you'll usually have the choice of synchronous or asynchronous writes.  With synchronous writes, the original writer won't get ack'd until both devices have received and written the information.  This is the only way to guarantee zero loss, but it has a (big) downside of increased latency. 

With asynchronous writes, the local storage will ack immediately, and then replicate to its partner (or possibly it will do it on a schedule, such as hourly).  This results in the potential for some data loss, though obviously less than a daily backup.

I haven't seen this functionality in home/SOHO NAS devices, though I haven't explored many.  Building your own asynchronous writers is relatively trivial (using rsync, bittorrent, et al), but synchronous writing requires some low level development.

[Ironman]

Hi Fred, this would be for business use. I sent WD an email today asking questions about their EX4 units.

It's sounds relatively simple but I've yet to find an "out of the box" solution.

[richado]

Synology, QNAP, etc.  All the major NAS vendors have this functionality, even on the low-end devices (and pretty much use rsync to do it).

[Ironman]

Thanks, I heard back from WD today and I think we will be buying a couple of their NAS boxes.