Hello yeowkm99,

You are going to want to select all the space as usable storage. 

so does this means cannot have seperate partition or LUN in the VSAN storage ?

Just out of curiosity, what would you use the other space for?    I don't think there's any advantage to splitting up into multiple vsans at that storage level, and I'm drawing a blank for other uses for the extra storage if you do carve some out.

we are thinking our doing MS Windows clustering on some of the VM on the VxRail system whereby we need a separate datastore for the clustering VM.