HuHa

For one thing, QDirStat explicitly tells you ">23.1 TB", i.e. MORE THAN 23.1 TB because it could not read all directories below /data/appdata, probably because of insufficient permissions. The part of the screenshot that was cut off (below the tree) also notified you of that. But even then there will probably be a mismatch because of ZFS snapshots which, like Btrfs snapshots, also are not reported by ZFS to the relevant system calls like stat(). You will need dedicated ZFS tools to give you that information. HTH HuHa QDirStat author

Also please notice that QDirStat uses 1024-based units, i.e. 1 kB = 1024 Bytes, 1 MB = 1024 kB, 1 GB = 1024 MB. In the latest versions, a right click on the size column will show you the size in Bytes.

Look closely: It says ">350.5 GB", i.e. MORE THAN 350.5 GB. In most cases, that means that you don't have permissions to scan some of the directories. In recent versions (no older than 2 years, V1.6.1 or newer; current: 1.8), QDirStat explicitly also tells you that.