Just freshly installed Windows 10 on P50. What to do with the previous disk?

[i2000s]

So, I got a chance to do a fresh installation of Windows 10 on a new SSD to my Thinkpad P50 machine. I put the previous 500GB HDD as a second disk for storage in parallel with the newly installed 480GB SSD. The new Windows 10 boots normally and can still recognizes the HDD as partition C which has Windows 10 pre-installed. I feel there may be MBR/loading partition and recovery partitions in the HDD, and it doesn't allow me to shrink the single partition C on the HDD to a smaller partition. I guess I cannot directly format the entire HDD, correct? How can I best use the HDD for storage and for future upgrades of more coming SSDs?

Thanks!
PS: Photo is here https://www.flickr.com/photos/52606482@ ... ed-public/

[RealBlackStuff]

Try diskmgmt.msc to first delete all the old partitions on that HD, and then format the whole lot in one go.
If that fails, put that HD in a USB enclosure, hook that up to any other laptop or PC that is not running W10 and run diskmgmt there.

[brchan]

Another option to format the disk is to boot off of a linux live distro and simply run gparted (gui) or fdisk (cmd) on the appropriate drive. You avoid the hassle of having to put the HDD in a usb enclosure.

[i2000s]

Another option to format the disk is to boot off of a linux live distro and simply run gparted (gui) or fdisk (cmd) on the appropriate drive. You avoid the hassle of having to put the HDD in a usb enclosure.

Finally, I have installed the Ubuntu 16.04 on the SSD (haven't figured out how to make the second monitor connected) alongside with Win 10, and formatted the HDD for storage from the Live CD (USB). I set up a LVM system on the SSD for Linux so that if I need to extend the space, I can cross the border and expand from the HDD to the linux system in the future. It could also be possible to upgrade with another set of SSDs.

Thank you guys, I have applied your suggestions with min trouble