Using your Mac as a networked Time Machine drive on High Sierra

How many times have you forgot to plug the external hard drive into your Mac, only for your scheduled Time Machine backup to fail as a result?

Creating a backup is one of those annoying tasks that’s easy to keep putting off, especially if you need to attach an external hard drive to your Mac every single time you create a backup. But if something does go wrong with your Mac and you wind up losing days, weeks, or even months worth of data, then you’re going to regret falling behind on your Time Machine backups!

In previous releases of macOS, you could setup macOS Server on a “host” Mac and then share a mounted hard drive as a Time Machine disk over the network – but in High Sierra this functionality is now built-in.

If you have access to two Macs that are running High Sierra, then you can create a shared folder on the host Mac, and then setup the “client” Mac to automatically backup its data to this shared folder. This is much easier than having to invest time and effort into setting up macOS Server, plus it doesn’t require you to download any additional software!

In this article, I’m going to show how to turn your Mac into a centralised backup for one, or even multiple Macs on the same network.

Since this technique requires multiple Macs, it’s particularly well-suited to places such as offices and schools, but it can also come in handy if you have an old Mac laying around, that you want to repurpose as your own personal Time Machine repository.

Creating a shared folder

The first step is creating a folder on the host Mac, that other Macs will be able to access. For the best results, the host Mac should be permanently switched on and connected to the network, as this ensures the client Mac(s) will always be able to backup their data to the shared folder.

On your host Mac:

  • Click the ‘Apple’ logo in the Mac menu bar.
  • Select ‘System preferences… > Sharing.’
  • In the left hand menu, find ‘File Sharing’ and select its accompanying checkbox.
  • Select ‘Options’ and make sure the ‘Share files and folders using SMB’ checkbox is selected.
  • Create a new folder by clicking the little ‘+’ icon underneath the ‘Shared Folders’ list.
  • In the subsequent Finder window, navigate to the location where you want to create this folder, and then click ‘New Folder.’
  • Give your folder a descriptive name (I’m using ‘Time Machine Backups’) and then click ‘Create,’ followed by ‘Add.’ This folder will now be added to your shared folders list.
  • Since this folder is where you’ll be storing your Time Machine backups, eventually it may contain sensitive data and content from other Macs. If multiple people use your host Mac, then you may want to restrict who can access this folder. Control-click the shared folder, select ‘Get Info,’ scroll to the ‘Sharing & Permissions’ section and then specify which user accounts have read and write access. Once you’ve finished, close the ‘Get Info’ menu.
  • Back in the main ‘System preferences… > Sharing’ menu, Control-click your shared folder and select ‘Advanced Options…’

  • Select the ‘Share as a Time Machine backup destination’ checkbox.

  • By default, Time Machine will consume more and more space until you have a hard drive that’s full of nothing but backups. Most of the time, you’ll want to limit how many bytes Time Machine can use for its backups, by selecting the ‘Limit backups to…’ checkbox and then setting an upper limit. Once macOS reaches this limit, it’ll start replacing older backups with newer ones, although note that if multiple Macs are backing up data to this machine, then this is the total limit for all these Macs combined.

Connect the client to the host

Once you’ve created a shared folder, you’ll need to connect all of your client Macs to the host Mac.

On your client Mac:

  • Open a new ‘Finder’ window.
  • Your host Mac should appear automatically in the left-hand menu, under the ‘Shared’ heading; select it.
  • Select the ‘Connect As…’ button in the upper-right corner of the Finder window.
  • If macOS asks you to authenticate the connection, then enter the username and password of an account that’s associated with your host Mac.
  • Navigate to ‘System preferences… > Time Machine.’
  • Click the ‘Select Backup Disk…’ button.
  • You should see your shared folder as an option, select it, and then click ‘Use Disk.’
  • Back in the main ‘System preferences… > Time Machine’ menu, make sure the ‘Back Up Automatically’ checkbox is selected, and from this point onwards, your Time Machine backups will be saved to this remote, shared folder automatically.

Repeat this process for any additional Macs that should store their backups to this shared folder.

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