Disk usage discrepancy?

Hi guys, I have a node which displays far less used disk space than the actual disk usage while checking with ncdu. The used disk space is just 4.05TB (out of 5.9TB allocated). But I check the node real usage with ncdu command and it shows the blobs directory with 10.6TiB. The disk is almost full. Why the heck is that? What should I do? Thank you!