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As explained by Dropbox, Smart Sync is a feature "that helps you save space on your hard drive. Access every file and folder in your Dropbox account from your computer, using virtually no hard drive space. ... With Smart Sync, content on your computer is available as either online-only, local, or in mixed state folders."

Last night and this morning, I moved a large quantity of files from an external disk into Dropbox folders on my MacBook (MacOS Mojave Version 10.14.4), then selected those Dropbox folders to be "online-only". The files rather quickly synched with Dropbox on the cloud -- I saw them appear in the local folders of a desktop computer that shares the dropbox -- but the grey icons (for "online only") took a long time to display in Finder. (More than twenty hours later, two larger folders still show the blue icon, for "synching", even though their contents have long appeared on the other computer.)

With growing alarm, I watched as each new directory added to Dropbox ratcheted up the amount of space used on the MacBook to dangerous levels (93%) even as large directories marked as "online only" continued to sync to the Dropbox cloud. I could only restore available space by moving some content back to an external disk.

Confusingly, information about how much space really remained was inconsistent. df showed 58 GB available:

Filesystem    1G-blocks       Used  Available Capacity Mounted on
/dev/disk1s1        465        403         58      88% /

while About this Mac => Storage showed 232 GB available.

According to one source, "the Storage tab in About This Mac ... can be useful as it is the only guide to what types of data are taking up storage space, but when you want to know how much space is used or free on any volume or disk, use Disk Utility: it’s much more likely to be accurate." Confusingly, however, my Disk Utility displayed both results:

  • 433.68 GB used, 3.95 GB on other volumes, 62.45 GB free
  • Capacity 500.07 GB, Available: 232 GB (169.55 GB purgeable), Used: 433 GB

As explained by Dropbox, "setting files to be online only will free up space on your hard drive within minutes (as long as your computer is online and able to sync to Dropbox). However: ... macOS 10.13 (High Sierra) uses ... APFS. With APFS, the operating system takes snapshots of the file system and available hard drive space. These snapshots may not update after you've used Smart Sync to set Dropbox files as online only. This means that hard drive space you freed up with Smart Sync may not be immediately reflected or available if this snapshot hasn't updated. This hard drive space should eventually be freed up by the OS, but the amount of time this will take can vary. This isn't a behavior specific to Dropbox, but instead the designed behavior of macOS." On APFS, the placeholders for "online-only files use a small amount of space on your hard drive to store information about the file, such as its name and size. This uses less space than the full file." Indeed, files marked as "online-only" continue to show their non-zero (online) sizes (e.g., with ls and os.path.getsize()) as if they were still available locally.

I gather this is a MacOS (i.e., APFS) issue, not specific to Dropbox.

My question: If Disk Utility shows 232 GB "available" but only 62.45 GB "free", what are the consequences? Would bad things happen if I were to add another 100 GB of files to the disk?

I am of course reluctant to add more content than space free just "as an experiment" but see how this could happen unintentionally.

Tom Baker
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  • Update, 10 hours after posting: Disk Utility now shows: 301.71 GB Used and **194.41 GB Free** and **228.35 GB Available** (33.94 GB purgeable). The two large folders marked for "online-only" still show blue icons, even though they seem to have synched over 24 hours ago. – Tom Baker Apr 08 '19 at 06:37
  • I can relate. I have enabled Smart Sync two days ago and Dropbox has been syncing ever since. I have removed almost 100 GB (outside my Dropbox folder) because Dropbox refused continue with syncing process because my disk was "full". The sync is now complete and I have the following numbers: *Capacity: 499,96 GB, available: 269,29 GB (250,79 GB purgeable). I have almost no "online-only" files and still 250 GB purgeable... – Thomas Bormans Jun 14 '19 at 11:01
  • @TomBaker, how are things now a few months later? Does everything admit to being sync'd? Have you had any problems that occurred after the first few days? – Paul Sep 29 '19 at 19:01
  • @Paul I have worked around the problem: minimal use of Smart Sync, which is inconvenient for other reasons (e.g., `/usr/bin/find`). I have other issues with Dropbox (e.g., how it handles symbolic links), so I may move away from Dropbox entirely. – Tom Baker Oct 02 '19 at 06:54

1 Answers1

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THIS HELPED ME: https://www.cbackup.com/articles/dropbox-taking-up-space-on-mac-6688.hmtl.html#A1

Solution 4. Clear the Dropbox cache folder Generally, there is a hidden folder that containing Dropbox cache stored in your Dropbox root folder, named ".dropbox.cache". Only when the function of viewing hidden files and folders is enabled in the operating system, you can see the folder.

If you delete a large number of files from Dropbox, but the hard drive of your computer does not reflect these deletions, the deleted files may be saved in the cache folder. So, you can manually clear the cache to clear some space on the hard drive by following the steps below:

  1. Open the Finder and select Go to folder... from the Go menu.

  2. A dialog box should appear. Now copy and paste the following line into the box and press the return key:

~/Dropbox/.dropbox.cache

  1. This will take you directly to the Dropbox cache folder. Delete the files in your cache by dragging them out of the Dropbox cache folder and into your Trash.
Stephanie L
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