If I move my home folder to an external SSD, what happens to the system data?

rogercorke wrote:

Well, well. I seem to have stirred up a hornet's nest here. Four replies from people - all proclaiming that moving your home folder to an external SSD will result in Armageddon.

Given that there are thousands of Mac users out there who put their home folder on an external SSD to save paying Apple's ridiculous prices for storage, would anyone who has done this like to comment?

You have been given consistent advice by highly experienced Mac users. If you want to ignore that advice, that's your choice and you accept the risk of hosing your system sooner or later.

I doubt there are "thousands of Mac users out there who put their home folder on an external SSD". But I *can* tell you we have lost count of the numbers of users who moved their home folder only to brick their Mac, lose their data and come here hoping to recover. And, sadly, many of them also never bothered to back up their data.

If you go to Settings > General > About > Storage Settings you can get a storage report about your system. And if you click the help icon (the "?") you can see Apple's definitions of the storage categories. Here is what it says about System Data:

"System Data: Contains files that don’t fall into the categories listed here. This category primarily includes files and data used by the system, such as log files, caches, VM files, and other runtime system resources. Also included are temporary files, fonts, app support files, and plug-ins. You can’t manage the contents of this category. The contents are managed by macOS, and the category varies in size depending on the current state of your Mac. You can manage your data that falls outside the other categories using the Finder or the third-party apps that created it."

In the above quote, the "don't fall into the categories listed here" refers to the other categories that are listed before System Data.

Some System Data is in your user home folder, primarily in the hidden user Library. Other System Data is in macOS itself; the system's /System and /Library folders; and the hidden volumes Preboot, Recovery & VM.

If you really want to drill down into details about what's taking up disk space on your Mac, get a copy of Daisy Disk from either the app vendor or the App Store. $9.99 both places.

If you want to read up on what Daisy Disk does, and how to use it, see the User Guide.

rogercorke wrote:

I am just moving over to a new MacMini and I am going to use an external SSD for my home folder.

Moving your user home folder to an external drive is not a good idea. The system expects your home folder to be on the internal (system) drive especially if it's the only user account, which is also your main admin account. There is a lot of stuff in the hidden Library folder in your home folder that the system and apps depend upon.

If your goal is to keep most of your user data on the external drive, you can achieve that without moving your user home folder. None of this *needs* to be in your user home folder.

• Music, TV & Photos libraries can easily be relocated to an external drive. Instructions are available in each of those apps' user guides and people here can also tell you how to do it.
• iMovie, Final Cut, Lightroom, CaptureOne and other app libraries/catalogs can can be created and/or relocated to an external drive.
• Lightroom, CaptureOne, Bridge and other image catalogs can be saved to an external drive.
• Browser preferences can be set to save downloads to a folder on an external drive
• And finally, nearly all apps can save to any disk or folder you specify including an external drive.

Here's what I do. On my external drive I duplicate the folder structure of a basic user home folder. I then point the appropriate apps to those folders. With apps like Word, Excel and other apps that don't have libraries, when I need to save a file I simply direct it to save to a location on the external drive.

• Documents
• Downloads (for browser downloads)
• Pictures (for Photos library)
• Music (for Music library)
• TV (for TV library)
• plus other folders that are unique to my needs
  • Movies - for iMovie libraries
  • Family History - for genealogy database & files
  • Catalogs - for LR & CaptureOne catalogs
  • etc.

First uninstall CleanMyMac, on these forums it is considered malware for multiple reasons including

a) it does absolutely nothing that Mac OS does not do on its own.

b) it modifies and damages Mac OS so that Mac OS appears buggy, creates odd behaviors and makes Mac OS slow.

If your system has not exhibited those behaviors yet, it will. On these forums you will find hundreds of other user that have had issues with CMM.

Once you have followed the developers instructions for uninstalling then restart the computer in Safe Mode and run an EtreCheck report and analyze the report to verify there is ZERO mention of CMM.

Regarding your original question, please DO NOT move Mac OS folders around until you have an extremely thorough understanding of Mac OS. If you ignore this advice there is an excellent chance you will brick the computer!!!!!!!!

If you bought a MM with in-adequate storage space, then return it and buy one with at least 1TB of internal storage.

You have been advised by multiple experienced users. You likely going to end up with a huge mess and go past the return time frame before you are able to get an adequately configured MM. It's your machine, your time and your money.

When it comes to buying a Mac it's not about buying the lowest cost configuration, it's about buying the configuration that best suits your needs. Many years of experience has taught well experienced users that long after the money is spent, users don't think about how much they spent, they think about the experience they are having at that point in time. Buy an adequately configured machine and that experience will be good, don't and well we cannot promise if the experience will be good or not.

In addition to the app @MartinR mentioned, there are also a couple free alternatives.

The first is Omni Disk Sweeper. it scans a drive and creates a hierarchical listing of all the folders and files on a drive with how much space they utilize.

The second is Grand Perspective. It is a graphical display of disk usage similar to Daisy Disk but in more of a block form and as stated is free.

The only area of your disk you should touch in terms of making room is in your home folder. Located in your home folder is a usually hidden Library folder. This folder contains all preferences, user configurations, user related app data and libraries, etc. and can get quite large. Removing anything there should only be done after researching the items contained within from app developers. Somethings can be removed such as caches but somethings cannot be removed regardless of how large they get. Only the app vendors can verify what can and cannot be removed.

I also strongly recommend getting rid of the CMM junkware as per the developers directions.

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Do not move your home folder as it will cause problems.

Like Martin suggests, move your Photos, Music, Movies and other Libraries to an external SSD.

Move your Photos library to save space on your Mac - Apple Support

Change where your music files are stored on Mac - Apple Support

Move your iMovie for Mac library - Apple Support

Move a Final Cut Pro library - Apple Support

However keep in mind, that to protect your user Libraries you should use two external SSD's.

One external SSD for your Libraries and a second external SSD to backup the Libraries.

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Another option if you want to keep everything under one roof.

Is to install macOS on an external SSD, then startup and migrate everything from your Mac to the external SSD.

Use an external SSD as your startup disk … - Apple Community

rogercorke wrote:

Well, well. I seem to have stirred up a hornet's nest here. Four replies from people - all proclaiming that moving your home folder to an external SSD will result in Armageddon.

As others have already mentioned, we have seen lots of users report issues after a minor OS update path when relocating the home user folder to another drive. I recall starting to see these reports back when Monterey was released and have seen more since that time even with Ventura. At the time when this occurred with Monterey, those people with relocated home user folders spent weeks trying to fix the problem since the fix was not entirely obvious. IIRC, several different Monterey update patches broke this custom setup because it is not a configuration Apple tests. I find it is best not to deviate from Apple defaults these days. Keep in mind that Apple does not provide any official documentation to relocate the home user folder.....the only instructions are for renaming the home user folder and the short user name.

If you go through with relocating the home user folder, then to minimize the chance of such a huge issue, you should make sure to retain the original home user folder on the internal boot drive as well as having a second macOS admin user account available that remains entirely on the internal boot drive.

If you are able to deal with spending time trying to fix this custom configuration when it breaks, then by all means go for it. However, I find things tend to break at the most inconvenient times. Most people want a stable system.

I think it is much easier to follow the advice of the other contributors to relocate the large libraries. If you are not using any apps that are using those libraries, then relocate all of your large data to the external drive. Many third party apps allow you to customize where their large libraries & project folders are located.

Given that there are thousands of Mac users out there who put their home folder on an external SSD to save paying Apple's ridiculous prices for storage, would anyone who has done this like to comment?

You should probably ask those thousands of users you found who have done so.

By the way, given that none of the replies answered my original question, I still need an answer to it.

To be precise, I've got 585 GB of System Data on the hard disc of my existing Mac Mini. Where will it go if I put my home folder on an external SSD when I transfer over to my new 256GB Mac Mini? In fact, what is on that System Data? I've cleaned off everything I can think of and it's still there. Anyone an ideas how I can get rid of it?

People who have performed a clean install of macOS and restored from backup have reported the System Data size is Ok immediately after the process. I would only expect that to be temporary solution.

The System Data consists of a lot of different items all controlled by macOS. Probably the majority of it will follow the home user folder, but I cannot say for sure since I don't have such a configuration.

See the post by @etresoft here:

System Data Taking Over Half of My Mac’s -- etresoft - Apple Community

And @Old Toad within the same thread:

System Data Taking Over Half of My Mac’s -- Old Toad - Apple Community

Thanks for your advice but I'm not sure it's going to answer my question. I have already bought - on the advice of dozens of people online - a 256GB MacMini and a 2TB external disc to back up my files -

You only bought one 2TB external drive? Won't you need at least two of them? One for your planned relocated home user folder, and another one for the actual backups? It is usually best that the backup drive has at least 2x - 3x the storage capacity of all the data you will back up from all media.

If your System data is out of control you can erase your drive and reinstall all and that number should be reduced for a certain period of time but may grow later on.

rogercorke wrote:

Well, well. I seem to have stirred up a hornet's nest here. Four replies from people - all proclaiming that moving your home folder to an external SSD will result in Armageddon.

Given that there are thousands of Mac users out there who put their home folder on an external SSD to save paying Apple's ridiculous prices for storage, would anyone who has done this like to comment?

It's your Mac mini and you can experiment with that notion if you like.

Just be sure to have a good backup, because the next macOS update/upgrade will result in total armageddon.

By the way, given that none of the replies answered my original question, I still need an answer to it. To be precise, I've got 585 GB of System Data on the hard disc of my existing Mac Mini. Where will it go if I put my home folder on an external SSD when I transfer over to my new 256GB Mac Mini? In fact, what is on that System Data? I've cleaned off everything I can think of and it's still there. Anyone an ideas how I can get rid of it?

Actually all of the replies answered your question and offered relevant options:

1) return the Mac mini and buy with more internal storage space.

2) move your larger user Libraries to an external SSD.

3) move and run everything from an external SSD.

I have been booting from an external ssd for many years. It has never caused a problem. Currently, my external ssd is in a USB4 enclosure, but Thunderbolt3 also was fast enough. I connect the boot ssd directly to the computer, not through a hub.

Everything works normally, including syncing with iCloud. My most demanding application is processing 50 megapixel raw images.

Booting from the internal ssd while keeping the home folder on an external ssd probably would work similarly. Backups (especially bootable clones) are simpler if everything is on one drive though.

People make life complicated for themselves.

To boot from an external SSD/HDD simply set up your new Mac normally and then install macOS on the external and go through the "Welcome" setup process again.

Job done!

The internal will have its own System Data and the external will also have its own.