How to: Use Time Machine To Backup Multiple Mac Computers On A Single Hard Disk

Requirements:

• I have three mac computers (one iMac, one MacBook Pro and a Mini) that needs to be back up using Time Machine.
• I want to use one hard drive to back up all three computers wirelessly over WiFi

Solutions:

1. Make sure all macs are within the same WiFi network
2. Connect one 1 TB external harddrive to my Mac Mini because the mini is up 24/7 as server
3. Share the external drive and grant proper permission so that all other Mac can access the drive
4. On each Mac, go to Terminal and enter the following command:

   sudo defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1

5. Go to Time Machine Preference and select the network drive just shared and use it as back up disk 

The key here is set the Time Machine to use Network attached harddrive by type the command above. I got this tip from this post. 

Mission Completed!! All my macs are now being backup on the same drive wirelessly. Hope this tip can help you too.

Edit 1: Because multiple machine is being backup onto a single drive, you might want to reduce the frequency of backup so that your network won't be jammed.  By default, Time machine does not let you adjust the frequency and do it manually in the system launch file is not easy for normal user.  I found a tool that's build for just doing that.  I will share the link later.

Edit 2: Friend of mine just point out that if you have vmware running and the images are stored in your main drive which is being backup by Time Machine, you'd better exclude the images because Time Machine does not do incremental backup on disk images.  It does whole backup every time when it sees image is changed.   That will eat your backup hard drive storage very quickly especially if you use default Time Machine backup schedule which is every hour...