Jump to content

Changing a time machine hard drive


Recommended Posts

Hello, I wondered if there was any information available on changing the external time machine hard drive over to a new one please. I’ve googled but get varying instructions! Thank-You! 

Link to comment
Share on other sites

Yeah, it's pretty easy.

Before I hit you with instructions, is this new EHD, is it a SSD or a Traditional Spinning HD?

Link to comment
Share on other sites

Alright, that's a spinning EHD. Because 6TB SSD Drives are really-really expensive. This info will be important later.

Follow these instructions:

The first thing I want you to do, if you haven't already, is turn on the feature that allows you to see HDs and other "Mounted Devices" on your Mac Desktop. 

  • Open the Finder. The easiest way is to click the Smiley Face on your DockBar:


Screen Shot 2020-02-29 at 3.31.00 PM.png

  • Then head to the Finder Menu and select Preferences:

Screen Shot 2020-02-29 at 3.32.35 PM.png

  • Once there put checks next to these items and change the bottom to "Macintosh HD" if you want:

Screen Shot 2020-02-29 at 3.33.29 PM.png

  • From there, just click the Red Circle in the upper left corner to apply the changes.

After you make this change, things like the Macintosh HD, any External Drives, Memory Cards from Cameras that are in a Card Reader and even portable DVD Disks will all appear on the Mac Desktop. This makes accessing them a breeze and is one of the things that has always puzzled me on why this feature isn't turned on by default. For example:


Screen Shot 2020-11-01 at 11.32.41 AM.png

Part 2

  • First, as you saw in my example above, your new EHD should appear on the desktop, though it may not. Here is an example of currently Mounted Devices on my iMac. You should see something similar if you followed my steps above:

    Screen Shot 2020-11-01 at 11.32.41 AM.png

Now the fun begins! Let's get that new Hard Drive prepped for use on the Macintosh!!

  • Click your Applications Folder, then open Disk Utilities.
    • Head to  Applications Menu >> Utilities >> Disk Utilities.

Screen Shot 2020-02-29 at 3.27.22 PM.png

  • This is where your Disk Utilities might look slightly different. Anyway, here is mine:

    Screen Shot 2020-02-29 at 3.38.59 PM.png
  • While in your Disk Utilities Module, please make note of any additional Hard Drives listed in the left column. Pay special attention to the Hard Drives listed under the "External" Section. For this process, it is much safer to only have one EHD Mounted / Listed!
  • It is imperative that you  Eject and Remove ANY EXTERNAL HARD DRIVES THAT YOU DO NOT WANT TO ERASE!!!  Your Disk Utilities Window should appear as follows, with only ONE External HD listed, and no Time Machine Drive either:

    Screen Shot 2020-11-05 at 7.42.04 PM.png



Clicking on the WRONG EHD and then doing a Erase / Partition is a VERY BAD THING. This is why we only want one EHD Mounted. Macs are a real PITA when it comes to Data Recovery. Which is great if you are trying to get rid of things, bad for when you do something stupid, like I did...and delete pictures from the years 2007-2011.

I still haven't gotten everything back, even after all these years of knowledge. :(



  • You can Eject the EHD from Disk Utilities, just click the little up-arrow/line next to the drive you want to remove.


Part 3

  • First select the EHD that you want to Format for use on the Mac in the left column:

Screen Shot 2020-11-05 at 6.32.24 PM.png

  • Then click the Erase Button at the top:

Screen Shot 2020-11-05 at 6.34.35 PM.png

  • Your Window should appear similar to this. At this point, give your new EHD its official name. Make it something Obvious, like WD 3TB or Client File EHD 3TB. Something recognizable and simple. You can only have so many characters for the name, so keep it short and simple: 


  • Then click the UP/DOWN arrows on the right, in the Format Section. If this was originally a Windows EHD, it will more than likely say, Windows NT File System (NTFS):

  • A list will appear as follows:


    • For a Traditional Spinning Hard Drive, ONLY SELECT THE MacOS Extended (Journaled.) DO NOT SELECT the "Encrypted / Case Sensitive" Options!
    • For a Flash Based Hard Drive (i.e. SSD, m.2) choose APFS.
    • Please Note! DO NOT use APFS for a Traditional Hard Drive! DO NOT SELECT the "Encrypted / Case Sensitive" Options!
    • Again, it's either the "Mac OS Extended (Journaled)" or the plain "APFS." Do not use any other option. For the people that do use those options, have reasons to do so. For the 99.9999% of us out there, including myself, we want to keep our Partition Types as simple as possible.

  • For the majority of users doing this, your new External HD will most likely be the "Traditional / Spinning" type/kind, as SSD/m.2 Drives tend to be extremely expensive for capacities over 2TB. As time goes on, this will definitely change, but for now your Disk Utility Window should look something like this:


  • Simply Click the Erase Button and let the MacOS do its thing:

  • When finished, you might get a message from the MacOS asking if you want to use the EHD for Time Machine or not.
  • If this is a Data Drive, tell it NO!
  • Of course, if this EHD is meant for Time Machine, tell it "Yes."
  • (Thank YOU Captain Obvious for that "On-the-Spot Report." Back to you Jim...)

PLEASE NOTE!! You want to keep your Time Machine External Hard Drives separate from your normal day-to-day backups!

AGAIN, DO NOT USE YOUR TIME MACHINE EHDs as a normal Data Backup Drive, not matter how tempting it might be.  Trust me on this, your TM EHD should be used to back up the internal "Macintosh HD" only and not have it backup any externals.

Keep things simple when it comes to Time Machine Drives.


  • If everything goes as expected, and followed all of my instructions, you should see your new EHD mounted on the Mac Desktop:


  • You will also see it as follows in the Disk Utility Module of the MacOS:


Now if you have made it this far, open up Time Machine in the System Preference. Verify that the Time Machine Drive is correct by clicking "Select Disk."


Here is a screenshot of my Time Machine settings. The 12TB G-Drive is my Data Drive and my 4TB is my Time Machine Drive. If you already had an empty Macintosh EHD, you could select it to be a TM Drive by selecting it here. But since this is a Western Digital Drive, I'm thinking you have a stupid exFAT Partition and that's why Time Machine is giving you grief; Time Machine requires a Mac Partitioned / Formatted Drive in order for it to be used for Time Machine. Make sense? 


Link to comment
Share on other sites

Thanks Brian, I've read through the instructions... Just wondering, the reason I have a new EHD is because my old EHD that I used for time machine has stopped working. Do I need to transfer any information from that or simply unplug it and follow the instructions above? 

Thanks Jodie 

Link to comment
Share on other sites

Unplug the non-fuctioning TM Drive, and follow the instructions above. Basically, once it's done formatting, it will ask you if you want to use if for Time Machine. Tell it yes.

Also, your Time Machine Drive needs to be just that, a TM Drive only. Absolutely NO other data files on this drive.

I can't stress this enough.

Link to comment
Share on other sites

Hi Brian so I followed all the instructions with my new WD 6TB. I ejected all EHD apart from the new one. It came up as "My Book" and I changed the name to WD 6TB and put the correct format of Mac OS journaled when I clicked erase it immediately came up with erase failed in red letters. I thought I would try again and it is saying the only EHD is unmounted  disk3s2. I haven't called it this I've tried ejecting it and putting it back again but nothing works. No other EHDs are connected. 

is it faulty? 


Thanks Jodie 


Link to comment
Share on other sites

Alright, I just hooked up a brand-new EHD that I received for Christmas. I'm on macOS Big Sur. Here are screenshots:

First, open Disk Utility. (Duh! You already know this part.) Then select the EHD in the right column.



Right-click on the EHD and select get info.



Take a snip of the pop-up Window (Command + Shift + 4) and post it in this thread:



As you can see, the current file system is ExFAT, which is what we do not want. So I'm going to close out the "Get Info" Pop-up and Right Click on that drive in the left column. Then select "Erase."




A Pop-Up Box will appear, I want you to select Mac OS Extended (Journaled) for your EHD.

Do NOT check the "Case Sensitive, Encrypted" plain Mac OS Extended (Journaled) is perfectly fine. 



The pop-up box will appear once more, give it or change the name, in this case I just put a 1TB at the end, and then click Erase.


After a few seconds, it should have a "Operation Successful" Message.



Then simply close out the Disk Utility. Your new HD should appear on the Desktop, as per my instructions above.



See if you can access it. If you can, try creating a simple folder on it to verify read/write access.


If you can create a simple folder, great! We can then tell Time Machine to use this drive. It looks like Apple changed a few things and my instructions are a bit dated. Now, if you are getting an error message, I'd say something is wrong and that drive could be faulty. Before we continue on with Time Machine, let's have another go at that drive.

Oh, for those wondering, if you are going to be using an External HD for Time Machine Purposes, it needs to be Partitioned / Formatted with the Mac OS Extended (Journaled) setting. APFS WILL NOT WORK WITH TIME MACHINE.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Create New...