A DRS cluster has certain shared VMFS volume requirements.
Configure all managed hosts to use shared VMFS volumes.
Place the disks of all virtual machines on VMFS volumes that are accessible by source and destination hosts.
Ensure the VMFS volume is sufficiently large to store all virtual disks for your virtual machines.
Ensure all VMFS volumes on source and destination hosts use volume names, and all virtual machines use those volume names for specifying the virtual disks.
Virtual machine swap files also need to be on a VMFS accessible to source and destination hosts (just like
.vmdk virtual disk files). This requirement does not apply if all source and destination hosts are ESX Server 3.5 or higher and using host-local swap. In that case, vMotion with swap files on unshared storage is supported. Swap files are placed on a VMFS by default, but administrators might override the file location using advanced virtual machine configuration options.