I am sitting here at my M2 Mac mini (1TB boot drive, MacOS Sonoma 14.7.4) with Disk Utility and Carbon Copy Cloner open. I’m doing nothing but reading on Safari. As I sit here, I am watching the free space on by boot drive decrease, as shown by both of those apps. It was 41.73 GB when I started this paragraph. It is now 41.68 GB. (I am writing slowly as I figure out how to explain all this, so maybe about 5 minutes passed between readings.)
I’m doing this because free space has been declining rapidly and I cannot account for it. I have read previous discussions here, Glenn Fleishman’s articles on MacWorld, Howard Oakley’s articles, etc. I’m still mystified. Yesterday morning my free space was about 86 GB. By evening, it was down to about 53 GB, though I hadn’t added anything near that amount of data. Overnight, it dropped to about 43 GB, and as I noted, is still dropping as I sit here.
I use Time Machine, and the total private size of snapshots reported by Disk Utility is about 6 GB. I use Carbon Copy Cloner and have snapshots turned off. I have TechTool Pro Monitor running and Backblaze backup.
I had files in my trash, which was set to delete files after 30 days. I emptied it this morning. Also this morning I moved about 15 GB of files to an external disk; I understand that won’t be reflected for at least 24 hours.
But if my free space keeps dropping unaccountably, I’m fighting a losing battle. At some point I could have no user data but no free space.
I’m now at 41.62 GB. How long before the Mac starts failing for lack of sufficient free space?
Over the course of two months I went through loosing about 260 GB of space. (Grandperspective.app showed this as “Miscellaneous Used Space”. free: https://grandperspectiv.sourceforge.net/). Even after moving about 150GB to an external drive. Then moved to trash & emptied trash. The miscellaneous used space increased comparably, but no increase in free space.
Several apple tech calls. Apparently variations of this is on their agenda. The higher level tech call fixed something, but it came back. The final support call was very heavy handed on deleting stuff in the application support folder. But did find time machine snapshot of a drive I haven’t used in a year: it still kept making shopshots in the hope I’d reconnect. With that file deleted, in System Settings > General > Time machine that drive was removed.
In the end, I went from 32GB available (I was really nervous then) to now 430GB in the startup drive and 150GB of my media on a external dive.
Suggestion: open Activity Monitor, look at the Disk tab, click on the Bytes Written column heading to sort the listing - get it to show large values at the top. This might help to identify the process that is the culprit.
Thanks for the replies. My efforts yesterday to empty the trash and move some files off the disk have resulted in 115GB of free space, so I’m no longer worried about the Mac choking to death. I really don’t think I cleaned up that much in file space, so I’m not sure what happened. I’ll wait now and see if the creeping decrease of free space returns.
@clincoln My prior experience with Apple Support (on a different subject) was not positive, but if I can’t find the root cause, I’ll contact them.
@ashley I looked at Activity Monitor, but for disk storage it only shows cumulative values over some undefined period of time. It’s not helpful for this sort of problem.
Another thought – a long time ago, though in the Mac OS X era, I had something similar and it turned out that the software for a game controller was unhappy and responding by writing lots and lots of lines to one of the system log files over and over. I would hope that these days there’s something in place to prevent these logs from growing large enough to cost you disk space, but it might be worth going to /var/log (you have to use the Finder’s Go… Go to Folder… menu option to get there) and seeing if anything there is large, recently modified, and/or growing.
I was going to second this, due to something that happened to me a while ago. Like you, @LarryR, the space was vanishing before my eyes. The system was even warning me (almost constantly) that my 256GB drive was becoming full. I’m on Mojave 10.14.6.
When I opened Activity Monitor and sorted by Bytes Written, I noticed that a process called coresymbolicationd was responsible for gigabytes of data being written. I also noticed that it would happen every time I booted, then eventually stop.
Using a disk space utility (OmniDiskSweeper), I noticed that there was a cache located at /System/Library/Caches/com.apple.coresymbolicationd/, and I began to Google the problem. I found posts indicating that it was generally safe to delete this cache. I ultimately found this post.
It took me quite a while (months!) to work up the courage to actually delete it, but when I waited until the process stopped writing data and then executed the command mentioned in the post above, relief was immediate. Your mileage may vary, and do make sure to have your data backed up, but for me the problem has not returned. I do, however, have a sneaking suspicion that all those writes across my months of deliberating over the fix have taken their toll on the lifespan of the drive.
I don’t know if your situation is the same as what I experienced, but if it is I hope this helps.
In short, if looking in Activity Monitor didn’t seem to work for you, please do try rebooting before you open Activity Monitor and see if your results are any different.
I believe the values are cumulative, starting from zero when the process started. So for a process like Mail.app, the numbers shown are since you last started that app. If you quit the app, you’ll see it disappear from the list. If you relaunch it, you’ll see it reappear, with initial values of zero. Some processes don’t quit: like kernel_task (and launchd, I think), so the figures shown for those processes are since the machine was last rebooted.
I was hoping that a process might show up near the top of the list that you feel shouldn’t belong there, as William M. describes. A shame it hasn’t. Perhaps it will if the issue reappears?
If you identify a suspect at some point, View > Show Deltas for Process might perhaps be helpful. But usually in this kind of situation, I’m just carefully watching the numbers in Activity Monitor, looking for values that are changing rapidly (most of the time, most are not).
That makes sense, but I’m seeing zero values in both read and write for every process. Weird, right? I’m on a MBP M1 Pro, macOS 15.4.1, time since last boot 6 hours 20 minutes. There are 985 running processes, and every one of them is showing zero in Activity Monitor > Disk > Bytes Read and Bytes written. The summary display at the bottom of the window is showing both Reads in and Writes out activity.
Honestly, I think watching it will make you crazy. There’s probably some background process that’s writing data, perhaps temp data, that’s changing the number.
I’d just restart and check again in a day. If you’ve lost notably more space then, look into it more.
You could also try running GrandPerpsective or DaisyDisk or OmniDisksweeper to see if they can identify anything that’s large and growing larger.
I agree with Adam that watching this too much can make you crazy. However, when I bought my Power Mac G5 twenty years ago, I bungled something that started some now-forgotten app filling up memory invisibly in the background until I stumbled upon the problem and figured out how turn the thing off. It wasn’t malware, it was just misconfigured in some way I have long since forgotten.