===== How to unlock a VMFS =====

If your VMFS filesystem / Datastore is locked (grayed), unlock it by else
  * Unmap the LUN from all ESX, then remap again
  * reboot ESX servers one by one, it will be unlocked at ... latest 

https://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1002293