How can I stop disk space from disappearing?

coxorange wrote:

Good afternoon,

My Late 2015 iMac’s fusion drive broke a few years ago, and I didn't want to repair that old Mac. So since then I’ve only been using the SSD, with El Capitan 10.11.6. Upgrades from that didn't work, probably because there is no Fusion Drive anymore?

Did you completely erase the whole physical SSD after the Fusion Drive broke? If not, then that is most likely the problem for not being able to upgrade macOS.

macOS can be installed on that 120GB internal SSD up to macOS 11.x/12.x depending on the exact model.

You may first need to install macOS 10.13 High Sierra followed by any of the later supported versions of macOS.

How to download and install macOS - Apple Support

Create a bootable installer for macOS - Apple Support

I’m experiencing a very strange phenomenon in which the available SSD disk space is just mysteriously being eaten up over time. I started out with 120.47GB, and with the little stuff I have on that Mac I should still have 118.49GB – however, over the months, it just kept getting less and less with me doing absolutely nothing to cause this, leaving me now with only 645.3MB.

https://discussions.apple.com/content/attachment/48686402-0b42-445c-9c06-c353db3bf22d

I have no idea where the yellow “Other” bit in the image comes from, or where these files are even located.

This has happened a couple times now, and I’ve always had to wipe the entire drive to get my 120GB back, only for it to then start chipping away at them all over again.

This also cannot be caused by malware as I have only downloaded a couple of apps from the App Store and I don't use Time Machine on this Mac.

My first guess is iCloud file syncing or a third party cloud based file syncing service.

Second guess, is a web browser or web page. I recently had this happen suddenly. I quit & relaunched the browser, but had to end up deleting the browsing data (cache & application cache on Vivaldi browser) through the browser's interface menu. This appears to have stopped the problem for me.

Does anyone know how I can locate and delete all of these files – preferably also how I can stop them from generating in the first place?

You can try using OmniDiskSweeper to look for the largest files & folders.

Also, alternatively, to get more space, could I buy an external SSD for that Mac and install Monterey there?

That is an option since the USB3 interface on the 2015 iMac will allow for 500MB/s transfers which is the same as the internal Apple SSD.

I suggest first upgrading to macOS 10.13 before upgrading to Monterey assuming you have the Late-2015 model (otherwise Big Sur).

coxorange wrote:

Did you completely erase the whole physical SSD

I tried... I don't remember exactly what I did. Here is a screenshot of Disk Utility, how it looks now (I booted pressing alt+cmd+R, so it should have started recovering from internet with the latest possible macOS: Monterey):

I'd like to completely erase everything again, how can I make sure it's done correctly?

As I suspected, you are only using the internal SSD.

The question becomes why the Fusion Drive has been split. Did it occur due to a failing Hard Drive, or was it accidental when you erased the system to reinstall macOS?

Before doing anything, I highly recommend checking the health of the internal Hard Drive by running DriveDx (free trial period). Post the complete DriveDx text report here using the "Additional Text" icon which looks like a piece of paper on the forum editing toolbar. I'll check the health report to make sure the Hard Drive is Ok to use. After all why waste time starting over if the Hard Drive is failing?

If the Hard Drive is healthy, then you would follow the instructions in the following Apple article to create a Fusion Drive setup & reinstall macOS (This procedure will destroy all data on both internal drives, so make sure you have a good backup):

How to fix a split Fusion Drive - Apple Support

Why start with macOS 10.13 High Sierra first...?

You can install macOS 12.x Monterey directly.

Don't know about OmniDiskSweeper, but DaisyDisk found nothing.

As I wrote before DaisyDisk isn't able to find "Other", so it seems it's unaccessible to delete.

"Other" is a category. You will never find anything called "Other" unless you created a file/folder with the name "Other". Unfortunately the "Other" category is a very broad category for items that do not fit into any of the other categories. Here is a link with two posts which tries to explain the "Other" category (called "System Data" on later versions of macOS):

Explanation of "System Data" and "Other" macOS Storage Categories - Apple Community

Those two utilities, OmniDiskSweeper & DaisyDisk, are meant to make it easy to identify the location of the largest files & folders. After all you want to know why your drive is filling up. If you find the largest folders, then that folder will probably give you a clue.

coxorange wrote:

The loop, which stopped me from completing the Monterey installation (from an USB installer), indicates that not everything had been wiped out completely from the SSD.

What's the procedure to accomplish this?

Sorry for the delay in responding.

Install whatever OS you can using either Internet Recovery Mode or a bootable macOS USB installer. If you can boot macOS normally, then I highly recommend you create a bootable macOS 10.15 Catalina USB installer now while you still can. If you have multiple USB sticks, then I would also create a 10.13 High Sierra and 12.x Monterey USB installers as well.

When you boot the macOS installer (Internet Recovery Mode or USB installer), then select the whole physical SSD as GUID partition and MacOS Extended (Journaled) file system (not for macOS 12.x Monterey installer which must be GUID partition and APFS (top option) ). Within Disk Utility you may need to click "View" and select "Show All Devices" before the physical drives appear on the left pane of Disk Utility. I would even try to erase the internal Hard Drive as well.....not sure if it will erase because of the hardware failure, but worth a try.....just ignore the Hard Drive afterwards & give it a different name.

Quit Disk Utility and select "Reinstall macOS" option.

Just want to confirm that macOS 12.x Monterey was actually installed on this iMac at some point in the past? If not, was macOS 10.13 - 11.x ever installed in the past? FYI, installed is a different matter than "used" them.

Edit: Oh, and do not install any third party apps and do not migrate/restore anything to this system until you get macOS 12.x Monterey installed because a 120GB SSD is barely large enough for installing macOS onto it so you want to make sure you have at least 60GB+ of Free storage space for the install & upgrade of macOS.

I can't address it in detail but you should be able to run something newer than El Capitan on that Mac. I ran High Sierra on a 2012 iMac and could have gone at least an OS version or two higher. Fusion drive or not, there shouldn't be a problem with that, though when I upgraded mine at one point I did have to use a firmware updater.

There is no simple solution to "other" on a Mac and the documentation that Apple has up now doesn't even go back as far as El Capitan. Here's a few things I have:

See available storage space in System Information on Mac - Apple Support

See used and available storage space on your Mac [was: What is 'Other' and 'Purgeable' in About This Mac?] - System Information User Guide for Mac - Apple Support

"Other: 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."

What is "Other" and What Can I Do About I… - Apple Community

Mac Pro says startup disk is nearly full … - Apple Community

coxorange wrote:

I already had Sierra, Catalina and Monterey USB installers.

Made using the linked Apple instructions.

Many macOS (up to/including Monterey) were actually installed.

Good.

Wasn't the file system for macOS Monterey "APFS (Case-sensitive)"?

No. macOS only uses APFS case-insensitive (top option, likely not listed with any sensitivity).

The only time macOS actually uses the Case-sensitive option is with Time Machine backups. Don't ever use the Case-Sensitive file system options. Only a handful of people would ever need to even consider that option and only for very specific use cases (developers of multi-platform software is the only thing which comes to mind).

coxorange wrote:

Thanks for this info. Interesting. I double checked and indeed I have a pair of SanDisk 512GB USB 3.0 flash drives which are formatted as APFS (case-sensitive). Maybe I had looked up that format from an APFS drive which was used by Time Machine! They are nearly full and I only use them for copying (or replacing/deleting) files to them manually. Could this cause a problem...?

If they are a macOS boot drive, then yes using a Case Sensitive file system for the boot drive may cause problems because Apple likely doesn't test macOS on such a file system......and I am sure that third party developers do not test such a configuration.

If these are just data only drives, then the only problem you may encounter is when you transfer files to a Case Insensitive file system. If two files have the same characters in their name, then you will get a conflict. For example if you have the following files on a Case Sensitive file system.....you will encounter issues when transferring them to the same folder on a Case Insensitive file system:

MY File
My File
my file
MY FILE

These are all unique on a Case Sensitive file system, but are exactly the same name when used on a Case Insensitive file system.

coxorange wrote:

I guess I would get a warning or an auto-rename

Theoretically, yes....or it could just error out completely.