Mac mini M1 What can you store on an external HDD?


This may sound like a Newbie question even though I’ve used Macs for well over a decade, but I’ve had no real luck finding an answer out there in Search World.

My poor old late 2013 iMac is showing its age, so I am hoping to move to a Mac Mini at the end of this year (Finances don’t allow an earlier swap). I had a 2TB SSD put in the iMac some years ago, and have got very comfortable keeping all our Audio Books (110GB) plus Bootcamp (160GB) on this drive, plus loads of space to spare

I won’t be getting a 2TB Mac mini for sure! Maybe at most a 512 GB, but I’m really interested in what can & cannot be put on an external HDD. From what I’ve read, Books cannot be moved there (And so I guess its Library) so I will have to limit my downloaded Library for sure, but could Bootcamp be run on an external HDD? Do other apps like PixelMator run fine from an external HDD? And will Time Machine see the external HDD as part of the Mac mini for backups?

Thanks in advance for any replies :smiley:

Bootcamp won’t run on the M1, or any Apple silicon.

Time machine can use the external as a backup if you want, when first connected macOS still prompts if you’d like to use the drive for backup. Not being a time machine user, I can’t remember if TM allows only part of the drive to be used that way, or if you have to create separate volumes first.

Also not a pixelmator user, but any app should be able to use an external for where it’s data lives. You could also choose to boot off of an external, if you took that 2TB SSD out of the iMac and invested in an external case.

You can also boot M1 macs from external drives (with some caveats) so you could continue to use the 2TB drive as the main boot drive to remove any worries about badly designed apps that didn’t want to work with data not on the boot drive. I can’t imagine many that would.

Depending when you bought that SSD, and the type of connections an external enclosure supports, you might find that it is significantly slower than the internal storage in the M1 Mini. A quick search shows people posting M1 Mini disk tests returning 2700-2800 MB/s r/w speeds. Most SSDs before the current crop of NVMes would top out at ~250 MB/s on a good day. The high end NVMe I have hooked up to a 2017 iMac via Thunderbolt 3 peaks around 1500 MB/s. Booting from that external makes the whole machine fly compared to the internal Fusion drive (used as backup now).

I would try to use the internal drive for booting and anything that requires the fastest data access. Audio books should easily be stored on the external without being limited by transfer rates.

Also as a final note, if you’re waiting till then end of the year, there’s a good chance that the Mac Mini will be upgraded to an M2 by then, either giving you access to the newer processor or discounts on the M1 Mini (introduced in Nov 2020). Biggest change in my view for the M2 is increased memory bandwidth and the inclusion of the hardware media engines.


Anything can be put on an external drive, but some things are easy to move and others require a bit of hacking.

One thing you can do is move your home directory to the external volume:

  • Use the Finder to drag/drop the user’s home folder (e.g. /Users/pfredd) to its location on the external drive (e.g. /Volumes/usbdrive/Users/pfredd)
  • Open the Users & Groups system settings
  • Right-click on the user and select the advanced options
  • Change the home directory
  • Log out and log-in as the user you just changed. Confirm that the home folder is in the new location.
  • Leave the old home directory in its original location until you’re satisfied that the new location is working properly. Then you can delete it.

I think (but I’m not sure) that you can do this prior to migrating the content of your old system. Create the user’s account, move its home directory (which won’t have a lot of content) to external storage, then migrate that user.

See also Move Your Mac's Home Folder to a New Location

Note that if you move your home folder to an HDD, it may impact performance for some apps.

You should be able to move certain sub-folders under Library to external storage (e.g. /Volumes/usbdrive/Users/pfredd/Library/foo) and create a symlink in the old location that points to the new location.

I don’t know about Boot Camp. I’ve never used it.

Most apps should work fine from external volumes, but I would recommend installing them to the startup volume unless you really have no choice, because putting them on the HDD will hurt performance. Just store your documents on the HDD (e.g. in your home directory).

Time Machine should back up every volume not on its “exclude” list. External volumes are usually put on that list by default, but you can remove it, to permit it to make backups of that volume.

Note that if you make backups using other software (e.g. CCC or SuperDuper), you will need to update your workflow in order to back up both volumes. The best way to do this is probably best discussed in another thread.


I have lots of experience of putting data on external drives to allow for a smaller internal drive.

Items which are very easy to put on an external include Apple Photos Libs, Music media, Movies media (Apple TV), Parallels virtual machines.

I have also always put iDevice backups on external drives, but this is not quite so straightforward, requiring symlinks, but they can be large so worth doing (or just use iCloud backup).

I also put my Lightroom Cloudy library on an external with symlinks. This is not supported by Adobe but worked for three years without problem.

Doing the above enabled me to manage with 256GB internal but after that I have gone with 512GB.

While I had the 256GB iMac I often considered moving the whole Home Directory to an external but every time I researched it I drew back. I always opted for the simple solution of putting data on the external. I certainly wouldn’t do it on a laptop of course.

I would recommend that the external should be a USB 3,2 (10Gbps) or Thunderbolt (40Gbps) SSD device.

I don’t think Books libraries tend to be large so should be able to keep that internal.

I didn’t quite understand “And will Time Machine see the external HDD as part of the Mac mini for backups?”… yes you can backup anything on an external to your TM backup drive. Obviously don’t have TM volume on same drive as data it is backing up.


I agree with @mikebhm. Putting your entire user home on an external drive can get you into trouble. OTOH putting individual large libraries from within (music, photos, etc.) on an external is simple, low risk, and high reward. Make sure the external is not excluded from TM and your all your stuff will remain backed up.

Like @angusC points out, Boot Camp isn’t an option on M1/2 Macs so no worries about having to drag that along.


Thanks to everyone who replied, I know have a much better idea of what is possible and how to go about it. Very much appreciated :smiley:

Now really looking forward to the move!

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Could you please be more specific? My backup system is entirely automated. I run Time Machine and BackBlaze continuously and SuperDuper on scheduled weekly backups of my MBA internal drive. I have avoided moving data to a backup drive because I really do not understand and can’t envision how I would/could modify my three backup methods to also include the data moved to an external drive.

Having all one’s data on the internal, backing up to an external (or two) is obviously straightforward and desirable…if it fits. If it doesn’t and you need to put say 500 GB of data onto an external you need to provision additional storage to backup that 500GB, so probably an extra 1TB for backups.

  1. You can add it to the same Time Machine backup as your internal by managing the exclusions in your Time Machine preferences, provided the TM backup drive is large enough.
  2. Adding an external to your BackBlaze backup is straightforward.
  3. You can also use SD to backup your data external to another volume on an another external, using a separate SD task.

There are multiple ways of configuring the destinations in such a setup, especially since the advent of APFS space sharing volumes within a container. There is no need to have separate containers for each backup volume.

The only no-no in configuring backups is not to have master data on the same physical drive as its backup.

I use two external drives for offloading a total of about 2TB of data, and each of those has two local backups and is also on Backblaze. I also have two computers, so it gets quiet complicated and I find it helpful to maintain a chart of what is where and what is being backed up to what.

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Thanks very much - excellent explanation!

I have deliberately and consistently stored all my data files (documents, photos, etc) on external drives with sets of RAID configured drives. Something I learnt from my computing days. It means that if something goes wrong with the computer, then the data files don’t go wrong or don’t disappear when the computer is being repaired. I backup my data drives to the cloud and it is easier to let the backup software focus on the external drives.