MBA M1 Drive Space Dropping At Random

July 30, 2022 2:47 PM

Something is causing my MacBook Air M1 (running Monterey 12.5) to rapidly drop drive space. I can go from 90GB free to 70GB without warning, then back again after a restart, and I cannot for the life of me figure out how to troubleshoot. The last time this happened it was because Adobe CC was trying to update in the background and had been writing tens of thousands of semi empty files to a hidden part of my drive, but I don't have Adobe on this laptop. What should I be looking for and where?
posted by The Adventure Begins to Technology (10 answers total)

Best answer: I use CleanMyMac to deal with this sort of thing - it will scan and dump junk files as well as looking for malware and a host of other stuff that eats drive space and slows my computer.
posted by leslies at 3:04 PM on July 30, 2022

Apple File System (APFS) uses snapshots to create backup copies of local data. I don't fully understand how this works, and what the purpose is. They are supposed to be created and reclaimed transparently, without the user having to worry about them. But they take up space.

Where did all that free space go on my APFS disk?

Managing snapshots: how to stop them eating free space.

View APFS snapshots in Disk Utility on Mac
posted by Winnie the Proust at 3:23 PM on July 30, 2022

APFS is black magic, as far as I'm concerned. One thing I've seen is that Time Machine keeps some hidden local backups which aren't cleaned out until you do an actual Time Machine backup.

[You should always be doing Time Machine backups, so let's assume you are, but haven't done it in a while... ahem.]

Does it get better if you force a new TM backup?
posted by soylent00FF00 at 4:25 PM on July 30, 2022 [1 favorite]

It could simply be using swap / virtual memory: that can happen if you have a lot of browser tabs open or some greedy extensions, or some other application that hoards memory.

Open Activity Monitor, check "swap used." Otherwise, DaisyDisk (paid) or GrandPerspective / Shorui (free) will give you a visualisation of what's using your disk space.
posted by holgate at 4:54 PM on July 30, 2022 [2 favorites]

Are you upgraded to the latest version of MacOS (Monterey)? If not, it might have downloaded the upgrade installer (in your applications folder) for the new version. That's maybe 20 GB.
posted by thechameleon at 5:21 PM on July 30, 2022

I see holgate already mentioned virtual memory. My MacBook Air used to eat up disk space for virtual memory until there was none left, then it would panic and tell me to close applications, but also wouldn't let me save files before doing so, because no disk space. Restarting always solved the problem, though (and I never actually lost data). Anyway: I can say from experience that 20GB can easily get used this way if you're running a hungry application.
posted by aws17576 at 7:37 PM on July 30, 2022 [1 favorite]

Check out the app GrandPerspective, it is my go-to for answering that exact question. Free/cheap, focused, no malware (unlike many of the “cleaner” apps).
posted by sixswitch at 12:29 AM on July 31, 2022

If you go to About this mac and look at the storage tab it might show where your storage is going.
posted by oldnumberseven at 3:37 AM on July 31, 2022

The one thing I noticed from poking at my time machine backups with BackupLoupe is that the /private/db/oah proactive translation database can balloon unpredictably as Rosetta goes off to see if there's any x86 binaries that need to be scanned. The whole process is a bit opaque, but it might be what you're seeing, too.
posted by Kyol at 6:34 AM on August 1, 2022

Response by poster: I ended up buying Clean My Mac which seemed to reveal a fair amount of drive space being allotted to Spotify's cache system. Deleting that folder got me 5GB back, and it looks like the abrupt loss/gain stuff has stopped. Thank you for that rec.

Also, I use Carbon Copy Cloner for backups, which I highly recommend as it creates bootable backups of your system that you can restore from! Time Machine only does files, which is good, but as mentioned up thread its snapshots can result in hidden bloat.

Grateful for guidance!
posted by The Adventure Begins at 12:09 PM on August 2, 2022 [1 favorite]