Here is a tool I’ve been dreaming about ever since I got really into btrfs snapshots for home and server backups: a sampling disk usage profiler! Unlike classical disk usage profilers, btdu doesn’t attempt to scan the directory tree starting from the top, but just picks random points on the disk and sees what’s on them.
One nice thing about btdu is that it starts showing results instantly. You only need 100 random samples to have a resolution of 1%, which is generally enough to know what ate your disk space. Even on very slow drives, resolving 100 samples takes very little time. It also works correctly with deduplication (snapshots / cloning) and compression.
More info and discussions: