If it does not show the new size with Unpartitioned Space at the end of the disk, then you will need to reboot. First try to right-click Disk Management and Rescan Disks. 
Dear All, We hava an R720xd server with a RAID5 array (PERC H710p RAID) . I've hot added a new HDD, and expanded the RAID5 array. It's been two days since the expansion has completed, but the OS have not recognize the new size of the disk yet, so I cannot resize the partition on it.  What did I miss? Is it just need a reboot?  OS: Windows Server 2012 R2  Thanks.  
PowerEdge RAID5 Expansion