I have been investigating NAS devices for a small office workgroup. All the documentation I have seen pays very little, if any, attention to backing up the data that is stored in the NAS device.

Does anyone here with experience of using NAS know if it is simple to duplicate or snapshot a NAS volume to another devices - preferably a USB disk (most NAS devices have USB connectors).

Some background. The workgroup currently has a small (old) file server (NT4) which provides email and file sharing. The workgroup is expanding from below 10 people to more than 10 people (NT4 is limited to 10 simultaneoous connections). Their data requirements are modest (currently ~ 50GB). Email would probably now be better served by an offsite IMAP service. That just leaves the file sharing. Linux aside(*), above 10 seats both Windows and OSX Server require full versions, which just for file sharing is overkill. NAS would do the job.

A suitable NAS solution would be a small 2 disk device in a RAID 1 (mirror) setup. That's fine for protecting against individual disk failure, but it won't protect against more catastrophic problems (e.g. fire/theft). Hence the need to be able to make regular backups of the disk.

An ideal situation would be to be able to reserve space on the 2 disks (or have a third disk in a 3+ disk device) to keep snapshots of the drives. And then to be able to regularly backup either the snapshots or the main drive image.

Is that feasible?

(*) I don't want to have to maintain a general purpose linux server. NAS devices themselves seem to be mostly linux but preconfigured for purpose and with NAS appropriate remote control software.