Beware Huge Caches with BitTorrent Sync

I’ve been using the excellent BitTorrent Sync app to keep some folders synchronized across my two Macs. I work mostly on my Mac Pro, but also do some work on my MacBook Pro. Also, when I write books and articles, I generally do the screenshots on the MacBook Pro, because it has a retina display. I dump them in a folder, which BitTorrent Sync then syncs to my Mac Pro.

I noticed recently that the space on my MacBook Pro’s SSD was shrinking. I looked through my files, and couldn’t find anything huge to delete. Then I looked at folder sizes, and saw that one of the folders I sync with BitTorrent Sync was more than 6 GB on my MacBook Pro; it was only 500 MB on the Mac Pro.

I looked inside the folder, checking invisible files. On OS X, invisible files and folders’ names start with a . or dot character; that’s what tells the Finder to hide them. There are several ways to view these invisible files: you can do so in Terminal, or you can use an FTP program to look at your local files. Or, to view them in the Finder, you can use this command in Terminal:

defaults write com.apple.finder AppleShowAllFiles YES

Paste that command in Terminal, then Option-click on the Finder icon in the Dock and choose Relaunch. Look inside any folders you’re syncing with Bittorent Sync for a folder called .SyncArchive. You could probably delete the folder, but I just opened the folder, selected all the files, and sent them to the Trash, then emptied the Trash.

Run this command in Terminal to hide hidden files:

defaults write com.apple.finder AppleShowAllFiles NO

Then re-launch the Finder as above.

As I said, this saved me over 6 GB on my MacBook Pro. I don’t know why so many files were being cached, and only on one of my two Macs. But I’m happy to have found the culprit.

Update: Thanks to the commenter who pointed out that there’s a setting for this. For each folder, click the Info button, then the Properties tab. Uncheck Store deleted files in SyncArchive. It doesn’t look like this deletes the folder, so you may still want to delete it manually.

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