DaisyDisk will not read the actual content of your private data, only the metadata (such as name and size). This approach is recommended in Apple's official WWDC 2018 video which mentions DaisyDisk as an example (begin at 9:22). Note that some small amount of hidden space (a few GB) may still remain even after scanning as administrator. DaisyDisk permanently removes files and folders instead of moving them to the system Trash, so that the disk space is actually recovered. These files cannot be undeleted, but there are other ways. Free space not appearing after deletion? Contrary to what you may expect, deleting files in macOS may not immediately produce free space.
This feature is not available in the Mac App Store version of DaisyDisk.
Daisydisk Still Hidden Spacecraft
Daisydisk Still Hidden Space Inside
Sometimes the amount of used
space on a disk may appear greater than the total size of all scanned files and folders on that disk. This is normal. The difference is usually taken by the file system overhead and system stuff like Spotlight index, but in certain cases a significant amount of disk space may be hiding in other users’ accounts or folders that are normally not visible to you. In order to reveal those folders you should scan the disk as administrator.
(hidden space) is a virtual disk map item that only appears when the total size of restricted files is significant, so you can see whether it’s worth rescanning the disk as administrator or not.
Large amounts of hidden disk space may also indicate to file system errors. Follow our troubleshooting guide for details.
In rare cases, a significant amount of disk space may still appear hidden even after scanning as administrator. This may be caused by problems with disk permissions. Try to repair permissions using the system Disk Utility app.
Strange hidden space may also be caused by a third-party backup application that created a temporary disk image and then terminated abnormally without cleaning it up. Use ls -la /Volumes/ command in Terminal app to check if this is the case.