duf (CLI)
A nice disk-usage/free-space display.
- User-friendly, colorful output
- Adjusts to your terminal's width
- Sort the results according to your needs
- Groups & filters devices
- Can conveniently output JSON
After installing the QPKG, login to your NAS via SSH, then run 'duf'.

Project source: https://github.com/muesli/duf
QPKG source: https://github.com/OneCDOnly/duf