My 2023 Macbook Pro running Tahoe 26.1 has 147.49GB of System Data. I have cleared all caches, deleted unused apps, and done a lot of searching to try to find the source.
Today I was transferring a ton of video from an old hard drive to Dropbox (over 100GB). Is it possible that this data is somehow being stored there while it syncs to Dropbox?
MacBook Pro 16″, macOS 26.1
This can absolutely happen. When you move huge files to Dropbox, it doesn’t upload them “in place.” Dropbox first stages them locally, indexing, hashing, creating block-level upload chunks, and all of that sits inside its hidden cache in ~/Library/CloudStorage or ~/Library/Application Support/Dropbox. macOS often lumps that temporary data into System Data, which is why it suddenly spikes right after a big transfer.
If the upload is still going, the cache won’t shrink yet. Once Dropbox finishes syncing, quit Dropbox completely and relaunch it, the cache usually collapses on its own. If it doesn’t, you can safely clear the Dropbox cache folder, but only after confirming the upload is 100% done.
This behavior is normal on Tahoe and newer macOS builds when cloud apps push large files around.
This can absolutely happen. When you move huge files to Dropbox, it doesn’t upload them “in place.” Dropbox first stages them locally, indexing, hashing, creating block-level upload chunks, and all of that sits inside its hidden cache in ~/Library/CloudStorage or ~/Library/Application Support/Dropbox. macOS often lumps that temporary data into System Data, which is why it suddenly spikes right after a big transfer.
If the upload is still going, the cache won’t shrink yet. Once Dropbox finishes syncing, quit Dropbox completely and relaunch it, the cache usually collapses on its own. If it doesn’t, you can safely clear the Dropbox cache folder, but only after confirming the upload is 100% done.
This behavior is normal on Tahoe and newer macOS builds when cloud apps push large files around.
Quite possible that it's due to a Dropbox cache in the ~/Library folder. As I mention in my user tip on reducing System Data, the cloud storage service I use for work keeps a 200 GB cache on my internal storage, though that's categorized by Spotlight/macOS as Applications.
How to free up ‘System Data’ and other st… - Apple Community
Excessive System Data after Hard Drive Transfers?
