Mountain Lion Time Machine can't reliably connect to LaCie 2big NAS I've been using a LaCie 2big NAS to back up my Macs for a year or two now, and it's generally worked fine. Now, however, we've got a couple of Mountain Lion Macs in the house, and it's stopped working. It takes forever to show up in the list of shares, and when it does, sometimes I can get my MacBook to back up to it, but often Time Machine just sits there for half an hour with a spinning barber pole and "Looking for backup disk". Sometimes this eventually results in a backup, but other times it doesn't.

I've seen some chatter on less reliable forums about AFP authentication changes in Lion and various system default settings you can change to get your Mac to accept older authentication methods, or whatever it is it doesn't like about the third-party NAS, but nothing I really trust. Can anyone help me out?

FWIW, one of our Mountain Lion Macs is running FileVault and the other one isn't, but they both seem unhappy with the NAS.
I have a LaCie drive running my Time Machine disk as well (Firewire connection). when I upgraded to Mountain Lion, I had similar issues as you are explaining.

Go to System Preferences, and click on Energy Saver (lightbulb icon under "Hardware"). On all Macs running Mountain Lion, especially the one connected to the LaCie NAS drive, make sure to uncheck "Put hard disks to sleep when possible".

This should fix your issue.