Just typing this on Terminal.app does not seem to work anymore.
defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1
So here is how I made it to work on Mavericks.
1. Execute the usual command above:
defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1
2. Create image file on local disk first because creating directly on NAS will fail
The image file naming seems important: name it [hostname]_[MACaddress] (the MAC address is without colons). So if the Mac's hostname is "mbp" and its MAC address is 12:34:56:78:9a:bc, then the file name will be mbp_123456789abc
You can check the hostname from Sharing settings.
Create the image as hard disk and of type sparse bundle. The size can be set anything, e.g., 100MB. Set volume name to arbitrary name, for example TimeMachine.
3. Copy the image file to NAS and expand it to the size you need for Time Machine, for example 300GB. Turn off Time Machine first because resizing seems to be always reset by Time Machine when it is on.
Use Disk Utilities to resize, or use hdutil from Terminal:
hdiutil resize -size 300g /Volumes/Backup/mbp_123456789abc.sparsebundle
4. Mount the image and initialize
Mount the image and initialize. The mount point, for example /Volumes/TimeMahine.
5. Set the volume as Time Machine destination
Now at this point even if you open Time Machine settings the volume won't show up. You have to set it from Terminal:
sudo tmutil setdestination /Volumes/TimeMachine
6. You are ready to start backing up using Time Machine!
Reference
