- The virtual disk must be eager zeroed thick; it cannot be zeroed thick or thin provisioned.
- Sharing is limited to 8 ESXi/ESX hosts with VMFS-3 (vSphere 4.x) and VMFS-5 (vSphere 5.x) and VMFS-6 in multi-writer mode.
- Hot adding a virtual disk removes Multi-Writer Flag.
UPDATE 2019-07-10: From vSphere 6.7 Update 1 onwards, the virtual disks sharing support in multi-writer has been extended to more than 8 hosts. In order to enable this feature, you need to enable /VMFS3/GBLAllowMW advance config option. For more info see https://kb.vmware.com/s/article/1034165