Disk usage discrepancy?

You also will need to restart the node after changing the configuration file.

Basically this will cause the node to go over all the files stored on the node and count their total size. Once done, it should update the storagenode databases to reflect what is actually stored on the node.
Disabling the lazy filewalker means it will run with standard I/O priority and not as a separate process with lower I/O priority.
You should be able to tell this is working by looking at the drive utilization - it should be pretty much at 100% until the node will go over all the files stored.

I also believe it should be mentioned in the log, some log message with “walk” in it.

And you probably should take a look at how to remove the decommissioned satellites data if you haven’t already, ideally before running the filewalker: