This will reformat your datastore, deleting all your VMs. You'll end up with larger block size, thus larger max virtual harddisk size.
Enable ssh (VSphere, Configuration, Software, Security Profile, Properties, Remote Tech Support (ssh), Options, Start, Start Automatically)
Find ID of device to reformat (VSphere, Summary, Datastore, select datastore, right click, Properties, resize extents, should be something like (naa.somerandomnumbers):3
SSH to ESXi.
Oh look, you can copy and paste it now
vmkfstools -C vmfs3 -b 8m -S YourDataStorename naa.somerandomnumbers:3