If you use tree quotas, you can use the quota report to determine how much space each share consumes.
If not, you might try VNX Monitoring and Reporting (VNX M&R), which is available for a free 30-day trial. There might be a way to leverage that. Otherwise, you'll want to look at a third-party tool like SolarWinds Storage Profiler.
Let us know if this helps!
thank you karl, quota trees are not used and it seems that I won't be allowed to instal a new tool, though VNX MR seems worth a try.
I will try to mount all exports as a root user and run du command on all sub directories to assess all sizes.
M&R will also just report what the file system tracks – not individual shares or directories
If you know that you need that often I would suggest to look at relocating into treequotas