Package: ncdu Version: 1.11-1 Severity: normal Hi! On filesystems that support copy-on-write, such as btrfs, ocfs2, zfs, ncdu will count shared space multiple times.
This is akin to already implemented hardlink detection, although for most filesystems it operates on extent rather than file level: if you reflink a 20GB file (like a VM image) then do 1MB worth of writes to one of the replicas, the total usage will be 20GB+1MB rather than 40GB. On Linux, you can get this information using FIEMAP. Use of "cp --reflink" isn't very widespread, but whole-subvolume snapshots are something most btrfs and zfs users do, so lacking this support in ncdu is quite jarring.
