MacBook M3 System Data full, no space for downloads

molinger wrote:

Two year old MacBook M3 with 1T drive. System data is taking up 668G...two thirds. Deleting items causes it to go up and so do not have enough space on the drive to download software to investigate or reinstall OS. All remedies I find do no help. Looking for ideas, thanks.

Try restarting your Mac in Safe Mode, as described here: Start up your Mac in safe mode - Apple Support

This will prevent most 3rd party system modifications from running. The last two people that I've seen report this problem have discovered that the Carbonite software was causing it. So Safe Mode should prevent that software from running and give you a chance to get ahead of it and delete some files.

After deleting files, it may take a day or so before the system finally cleans out the local snapshots that are holding those deleted files. You may be able to force the process by using Disk Utility > View > Show All Devices and then Show APFS Snapshots. Deleting those snapshots should give you back some space.

But all of this is merely to get ahead of the problem. Once you restart normally, it will likely return with a vengeance. You have to identify what software is causing it. I only mentioned Carbonite because two people recently identified it. But it could be literally anything. It could even be part of the operating system and Safe Mode might not help. But it can't hurt to get lucky!

molinger wrote:

Problem identified in that it was Carbonite. Spoke with an Apple support person who guided me to the Library folder and stated that I should look in each folder to ID the one with large data. Deleted the carbonate folder and ops are now normal.

Appreciate your update here molinger

I don't hear much about "Carbonite" these days. I am surprised it is still around as an option on th Mac; maybe it works better on a Windows machine(?)

What I remember from a decade(?) ago when I tried it— that it really was demanding, ramping up CPU and the fans. You would think by now it would be improved...

Could not delete it fast enough was my experience.

molinger wrote:

Two year old MacBook M3 with 1T drive. System data is taking up 668G...two thirds. Deleting items causes it to go up and so do not have enough space on the drive to download software to investigate or reinstall OS. All remedies I find do no help. Looking for ideas, thanks.

Call Customer Support (800) MY–APPLE (800–692–7753)

Outside the USA—Contact Apple for support and service by phone

See a list of Apple phone numbers around the world.

Contact Apple Support - Apple Support

molinger wrote:

None of these suggestions is showing promise yet.

You hadn't mentioned Carbonite then. The solution is pretty obvious - remove Carbonite.

Cannot wrap my head around the fact that, when I selected to move documents to the cloud, system data went up proportionally.

I'm not sure what you mean there. It could mean many things. What "cloud", for example? Did you try to move 1 TB of data to the cloud? That might be problematic, especially when you have some other cloud service that is going to work hard to fill up every byte as soon as you free it.

I am prone to ask myself, what has changed lately?

Is there even any way for you to find that out? Many apps these days have automatic updates. And people today are absolutely obsessed, addicted even, to updates. In many cases, they only want the current OS update and expect any 3rd part software from previous decades to run flawlessly. But many 3rd party apps know this and install their own auto-update mechanisms. So anything can break at any time with no notice.

read this article for additional guidance:

How to free up ‘System Data’ and other st… - Apple Community

"On the cloud" is great for sharing photos, but is not a viable backup solution for everything you have. The stuff is not under your control, and is subject to sloppy handling, arbitrary changes in policy, theft, accidental deletion, data loss [are they making frequent backups using best practices?], and discontinuation or throttling of the service. It can easily take three days to restore it at ordinary Internet speeds.

If you do not have a recent local, disk-based backup, your computer is like a ticking Time bomb. You are only one disk failure, one mainboard failure, one crazy software, or one "oops" away from losing EVERYTHING! Drives do not last forever. It is not a question of IF it will fail, only WHEN it will fail. In addition, you never know when crazy software or Pilot Error throws away far more than you intended.

If you are using another direct-to-disk backup method that you prefer, and you currently have a recent disk-based backup, that is great. If not, you should consider using Built-in Time Machine. Take steps to acquire an external drive as soon as possible. If you buy one, a drive 2 to 3 times or larger than your boot drive is preferable for long term trouble-free operation. Do not pay extra for a drive that is fast.  (You can get by for a while with a "found" smaller drive if necessary, but it will eventually become annoying).

Attach your external drive and use

Settings > General > Time machine ...

Back up your Mac with Time Machine - Apple Support