Success. I have moved my iTunes library onto the NAS and Time Machine is happily backing up to it as well. I’m not sure that the PC has access to anything, but to be honest, not sure that’s a problem – the PC isn’t used for much apart from keeping the rest of the family happy with facebook, streaming TV etc. I’ve never bothered doing a backup of it as there’s nothing on it that can be reinstalled or redownloaded. A hassle yes, but not going to lose family photos or anything.
Moving iTunes has cleared about 550G off the iMac, correspondingly the backup is significantly smaller. I’ve also freed up a USB port, which is always helpful.
The only drawback I’ve noticed is that the NAS isn’t as quiet as the iMac, must be the fans, and it does create a noticeable lag in my system. I suspect that is the trade off, noise reduction and sleeping drives in the NAS vs instant response in iTunes. I’ll fiddle with the settings as I use it to find the sweet spot for me.
Overall I’m happy with what’s happened. I’m not 100% sure I know why it started to work yesterday and that worries me a little. But I backups that I can restore to if required.
And later if I wanted to I could turn the server in a cloud, an ftp, a web server or whatever as well. But not at the moment.