Time Machine Sharing
 

I have an iMac that uses an external USB2 500GB drive to back up via Time Machine. I also have a MacBook Air – can I use the external HDD plugged into the iMac to share as a backup device using Time Machine on the MacBook Air over my wireless network?

I don't think so, I know Time Machine has to see the drive under 'Options' for it to be used as a Backup Device.

However I am not 100% sure! I will have to test it in our Mac Lab.

*Updated* - Yes you can use Time Machine over a network if your external drive is hooked to your iMac, and both are running Leopard.

You need to take the External Drive and make it visible on the network, give the correct read/write permissions.

Go on the MBA and mount the drive on your desktop.

Open up Time Machine and click 'Change Disk'. It should show up in the list of available drives.

how do you share an external among more than one mac wirelessly? how do you make one mac see it when it is not physically plugged into it? can this be done?

Once the drive is shared, any Mac computers on the same network can see the drive.