My mum has an iMac with a 3TB fusion drive in it and she's running out of space. She loves photo and video editing. She's good with final cut but not with managing separate storage. SSD's do not go up to that size and if they did, they'd be massively expensive. The fusion drive still uses regular storage under the hood for the majority of it as far as I can tell.

Would it be a good idea to move her home directory to a fast external hard drive? Say I get her a thunderbolt 3 capable hard drive with 8TB or 12TB, like the LaCie's. She doesn't have to try and manage several drives for her work, but she does have a ton of space afterwards. Are there any performance concerns or upgrade issues I should be aware of?

2 Answers 2


Moving the entire user domain, instead of just the folders for Videos and Photos may be overkill, though it would keep things simple. You're not going to see any advantage from moving preferences, audio files, Word docs, etc, as they are too small and not causing any bottleneck.

There's no disadvantage either, except that if the Mac boots up and can't find the drive, it will create a brand new (empty) user account on the system disk. "Where has all my stuff gone?"

Don't forget that you'll need another device to back up to!

Fusion drives can reduce in performance as they fill. I would recommend swapping one or more parts out for a regular SSD in due course.

  • Thanks for the heads up. Is it easy to re-attach the external home folder in case that happens? Is that something that happens frequently?
    – Jorg
    Jun 29, 2019 at 23:26
  • @Jorg It simply depends on the timing. As long as the drive is connected, ready and available when the system starts looking for the user home, then you'll be fine. It used to happen more on older systems. It can be a bit tricky to fix, as you are now using the empty account, and the other domain is supposed to be the same one. Always best to keep another admin account to log into (on the system disk), from where you can fix it.
    – benwiggy
    Jun 30, 2019 at 11:36

Do it!

I got a 2018 Mac Mini as a gift but only a 256GB drive. My user profile is almost that size. So I got a 1TB SSD and a nice USB-C/Thunderbolt case and copied the profile over there. Works a treat for me.

Once you have copied her profile to the external drive go into System Preferences > Users and Groups and Control Click on her user name and select Advanced Options. In there you can choose the user folder on the external drive.

Once that is done reboot and delete the old user folder.

With a nice fast drive with a quality case and a USB-C/Thunderbolt 3 interface she will not likely notice any slowdown at all.

Note that I didn't move the Applications (or any other) folder as I had enough room for those. While there is no officially supported way to move those folders to another location I believe you can still do it with a hard link. That is working for my Dropbox folder on another Mac just fine. And keeping everything else on the internal drive you should see little or no slowdowns due to system directories being elsewhere.

  • 1
    Yes. Fusion is optimized for the OS and caches for the system and splitting the user folder is best if you can’t just move some whole categories elsewhere. (Music / Photos / documents that don’t need to be in the home folder would be worthwhile smaller separations based on size totals.) I would say get the 8 for the live files and 12 for time machine to back everything up.
    – bmike
    Jun 29, 2019 at 3:36
  • Sometimes cleaning up the disk is also a good idea. I use tools like Daisy disk to do so. I’m always surprised to see how many old garbage it can find.
    – Xvolks
    Jun 29, 2019 at 6:37
  • Sweet! No I won't move the applications folder, it's not in the home drive anyway and a future upgrade to her iMac will include an SSD for sure so I'd like to keep them on the system drive. I was just wondering if it makes any impact on performance or upgrade difficulty :)
    – Jorg
    Jun 29, 2019 at 9:59
  • If you use Apple's Migration Assistant it doesn't care where everything is, it just sucks it from one Mac to the other and puts it in the default location. So you should be fine. Jun 29, 2019 at 17:57

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