Not able to add extent in Datastore

Hello Everyone,

                         I have my two ESXI's 6.7 running on individual machines.

The one is fine with the two HDD each of (1 TB)  added as an extent to Booting HDD(2 TB) comprising of single Datastore..

                         The real problem lies with the other ESXI 6.7 well, as i can't expand by adding extent with the booting HDD (2TB)..

Surprisingly, if i left the booting HDD 2TB as one Datastore and configure the other  HDD of 1TB as other Datastore individually, i can expand by adding extent to the later one

but not with the 2TB..

                          I have attached some pictures within this..

Any Help would be greatly appreciated..