You can create another virtual disk using disks on remaining slots and use as datastore to ESXi.  Installing another OS on new virtual disk will also work. Please note dual boot is not something which is validated on PowerEdge server hence we cannot guarantee that it will work.
Hi, I have a T410 server with a SAS 6/ir card installed with six HD slots. Slots one & two are configured with RAID 1 with slots three & four used as hot backups, and the remaining two slots are empty. An ESXi 6.5 host image, with virtual machines, is installed on the RAID 1 disk array as explained above. I have two questions: 1. Can the two remaining slots be used as a second boot disk (in a RAID 1 configuration) to run a standalone Windows, or Linux image directly by selecting it via the boot manager at start up? 2. Any unseen issues, if the remaining disks are used as an additional datastore (in a RAID 1 configuration) for the ESXi host image? This datastore will be use as virtual hard drive space for the virtual machines on ESXi host etc. lag
Can I use the remaining (2 empty slots) of a six bay SAS 6/ir as a second boot 
disk?