Hi allan, thanks for your reply and ideas. Here are the images hosted somewhere else, hope you see them now:
The funny thing is - I did not change any setting in BIOS before a new clean install of Windows. Before a clean install this feature was working fine. In order to format the drive I disabled acceleration first in the IRST. Afterwards clicked on Make Available and waited a little bit and I was able to format the drive. I was following the tutorial on forum.notebookreview.com/hp-pavilion-notebooks/676213-definitive-guide-clean-install-os-mssd-cache-equipped-laptop-dv6t-7000-dv7t-7000-envy17-3200-a.html (skipped the optional step 5).
I believe I already have the latest IRST installed - 12.9.0.1001.
