Upgrading Windows 7 x64 SP1 to Windows 10 on a system equipped with Intel Rapid Storage Technology (RST) failed with data-loss!
I've tried to upgrade my Lenovo Y580 with a 1 TB HDD and a 64 GB SSD (the SSD is hidden by the RST technology as a high-speed MRU-buffer for the HDD).
All seemed to go fine, until the upgrade process executed a reboot, and it couldn't find the boot-partition it had just upgraded.
All attempts to repair the partitions, reverting the installation or even using a Windows 7 SP1 boot-USB for recovery, didn't result in the partitions to be restored (at all) and rendered the laptop 'useless'.
Solution I applied was: Buy a Samsung 500 GB SSD (850 EVO), remove the 64 GB SSD (in an M.2 slot next to the SATA-connected HDD/SSD), re-installed Windows 7 x64 SP1 with all Lenovo drivers (they are on a separate, unharmed, partition of the HDD), and then upgrade to Windows 10.
Now I'm re-installing most generic applications I had previously installed, like browser, pdf-viewer etc.
Yes I'm working on recovering files from the damaged partition, but there where no really important files on it, all important stuff was backed up in the cloud, on USB sticks or on other PC's. It's a pity I don't have my browser history anymore, but that'll rebuild in the coming weeks/months So, long story short
: When upgrading a similar RST equipped PC, make images of your entire harddrive before attempting the in-place upgrade!