I discovered why “System Data” is taking up so much space on my SSD: there is a hidden file, in a hidden folder that is 53 GB in size: Users/.username/.username.sparsebundle. The file and folder were created a long time ago, but I am not sure why. It seems like this could be a Time Machine file, but I don’t use that program, although I possibly looked at it once. I suppose it is possible that Migration Assistant could have created the file as well.The only attraction I have to Mac clean up applications is the potential ability to do something about System Data problems. Of the 251 GB of flash storage on my iMac, 111 GB is currently taken up by System Data. Frustratingly, I cannot figure out what is taking up so much space. Fortunately, I still have 73 GB of available memory left, so I don’t have to solve this issue right away. However, for the first time, I think I will have to do a clean install to reclaim this space.
I downloaded a trial version CleanMyMac X, and readily found the file using the “Space Lens” feature of the program. Interestingly, EasyFind will find the file but does not report the size. Thus, listing the files in order of size didn’t help in locating this problem.
As you likely know, the MacOS included tools for locating large files (e.g., About this Mac>Storage>Manage>Large Files, or in Finder using File Size) won’t find this file because it is hidden.
Bottom line: Score 1 for CleanMyMac X.