Time Machine with external HD shared on another Mac

Discussion in 'macOS' started by maddin4j, Sep 18, 2011.

  1. maddin4j macrumors member

    Jul 28, 2009
    Hey everyone!

    I am on OS X Lion and I have a MacBook Pro (Early 2008) and a MacBook Air (mid 2011). An external hard drive is connected to my MBP and it is in the list of Share Folders in System Preferences under Sharing.

    I want to back up my MacBook Air using Time Machine by using the hard drive that is connected & shared by my MBP.

    However, when I choose a disk in Time Machine preferences I don't see the shared external hard drive.

    How do I back up over my wireless network?

  2. Ed78, Sep 19, 2011
    Last edited: Sep 19, 2011

    Ed78 macrumors newbie

    Sep 19, 2011
    I was trying to find the answer to this as well. I have a Mac Mini (MM) running Lion setup with an external drive that is used for Time Machine (TM) backups for the MM and my MacBook Pro (MBP) which is also running Lion. Previously, in Snow Leopard the MBP was able to select the MM's external drive as the TM backup location. After doing clean installs of Lion on both machines the MBP could never select the MM's external drive as it's TM backup location even though the MM's external drive was connected and usable in Finder. It just never showed up in the list of available drives when pressing "Select Disk" when truing to setup TM for the MBP.

    I tried various suggestions on the net to no avail (the pondini TM FAQs, and some others). Nothing worked and all posts I found was of course you can use another Mac's external drive as a shared drive for TM backups. I found a MacLife.com article for "How to Connect to External Macs via AFP in Lion" that shows how to connect to another Mac via AFP by using Finder's connect to server option. After connecting to the MM as a server I was then able to choose any of the MM's volumes and mount them on the MBP (note I had to disconnect the previous Finder mounted MM volumes first). I mounted the MM's external drive and then it was an option in the TM when pressing "Select Disk". I don't know why it previously just worked in Snow Leopard, but its probably due to the changes in Lion's AFP handling.

    Long story short do this:

    1) On the computer with the external drive you want to use as the TM backup (the MacBook Pro here) for the other computer open System Preferences and select the "Sharing" preferences. Make sure the "File Sharing" option is turned on. Note the AFP address for connecting to this destination computer such as "afp://".

    2) On the computer you need to backup (the MacBook Air here). Open a Finder window and make sure none of the destination's volumes (the MacBook Pro here) are already mounted. Select "Connect to Server" in Finder's Go menu (Command k) and then enter the AFP address for the destination computer from before and connect. When the list of mountable volumes appears choose at least the destination's external drive.

    3) Open TM on the computer your trying to setup (the MacBook Air) and choose "Select Disk". The external drive you just mounted should now be in the list of selectable drives for the TM backups. Then just setup the other TM options as needed.

    I hope this helps. I've been trying to figure this out for about a week when I got this working yesterday. It was driving me nuts because the drives wouldn't show up on my MBP running Lion and all the posts I found for using another computer's external drive as a shared Time Machine backup location indicated it should just work. So far things appear to be working just as they did in Snow Leopard. I don't know if this is just how it needs to be done in Lion or if there's a bug in Lion. All the TM support documents I've read suggest this is a common and supported method to use TM with multiple Macs. Note that I've repeatedly ran across postings that Apple Airport Extreme Base Stations that have a connected external drive is not a supported option for using TM.

    I'm not sure if all of the pondini Time Machine setup values are needed to have this working regularly, but you can check them out if needed. I've never used all of those settings in Snow Leopard or Lion and things have worked fine. I just have File Sharing turned on for the computer with the shared external drive and its been working normally.

    Pondini "22. How do I set up Time Machine to a shared drive on another Mac?" link:
  3. maddin4j thread starter macrumors member

    Jul 28, 2009
    Thanks for your reply! Unfortunately I have tried the steps you mentioned already and I tried them again after your post but no success. I have tried this with two different hard drives.

    I really don't know what's wrong. I found out a way for Time Machine to show unsupported drives via Terminal but backing up never works. All I get is this error message:


    I have no clue why. Both are just normal external hard drives. One connected via USB and the other uses FireWire 800.
  4. DustinT macrumors 68000


    Feb 26, 2011
    There is another solution. You can install Lion Server on your Macbook Pro and it will allow you to handle Time Machine backups automatically. You can easily run Lion Server on a machine you use for normal stuff.
  5. maddin4j thread starter macrumors member

    Jul 28, 2009
    Yes but I don't want to spend £35 on Lion Server just to get something to work that has apparently worked fine in Snow Leopard.
  6. DustinT macrumors 68000


    Feb 26, 2011
    That I do understand. :) I just thought I'd mention in case you weren't familiar with the idea.
  7. Ed78 macrumors newbie

    Sep 19, 2011
    If you connect to the MacBook Pro as a server you still are not able to select it's volumes for Time Machine backups on the MacBook Air? Or does it list it as an option and then you gets the error alert you posted?

    Are you able to connect and mount the MBP's volumes using the "Connect to server..." option in Finder?

    Make sure in the MBP's File Sharing that "Share files and folders using AFP" is turned on (there's an "Options..." button). It should be on by default. I also have SMB on as well although that should not make a difference.

    I also never turned the option to show unsupported drives for Time Machine backups on since I just want it to work.

    I agree with you that I prefer not to use Lion Server just for the purpose of Time Machine backups.

    I'm about to do the same thing with my dad's iMac/MBP setup to use the iMac's external drive as the MBP's Time Machine backup location. I'll post back if that works or not.
  8. pguffey macrumors newbie

    Mar 4, 2012
    I've got a similar situation - I can see the external drive on my macbook, I can write to it, and can even see it in time machine, but when I try to backup to it I get a message that it is not available???

    Any help appreciated...
  9. romeyn macrumors newbie

    Nov 1, 2009
    I'm having a similar problem. For over a year my MBP has been backing up to an external drive attached to a Mac Mini running OS X server. I attach via AFP file sharing, as this server's not on the same subnet as my MBP. This always worked. A couple of weeks ago my backups mysteriously stopped working. I'm just now getting around to trying to figure out why, and nothing I do works. The server's Lion. The MBP is Lion.

    I can mount the drive via AFP. The drive itself is a share point. I can write to it. But it doesn't show up as a usable volume in Time Machine prefs (even though Time Machine "remembers" it's supposed to use it.

    When TM tries to execute, I am informed that the backup volume can't be found. My backup set still appears on the drive and seems to be intact.

    I find myself wondering what's changed. It WAS working!!
  10. sgbirch macrumors newbie

    Apr 12, 2013
    Out of the box Time Machine does not allow you to back up to a network drive. It just doesn’t show up when you go to choose a backup disk. You have to run a command in Terminal first to enable this function. On the machine you want to be able to access a network drive open Terminal and enter this command to enable networked drives in Time Machine:

    defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1

    Ref: http://macstuff.beachdogs.org/blog/?p=59

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