On my newly built ESXI host I tried to build a new data store but it is not showing the second physical hard drive. It only shows Data Store 1. Dell did give me and ESXI Iso but I think I used the download from VMware instead and POSSIBLY the issue. Not sure. Server is a Dell R240 with 2 - 1TB hard drives that are not in a RAID
You need to provide more details, like the host hardware (e.g. server model, RAID controller, disks, disk configuration, ...).
André
Is the second disk listed in /dev/disks/ ?
From the GUI check whether the two disks show up as storage devices.
André
Not knowing your system configuration, I can just assume that the two disks are somehow connected to the server's internal S140 controller, which needs to be configured to present the disks to the operating system (ESXi).
André