When using ESXi (Embedded) in a VirtualCenter cluster with HA enabled, you’ll run into a problem with userworld swap. Every ESXi host needs this swap enabled. VMware KB 1004177 explains the steps needed to configure the scratch location.

This location can be a folder on an existing VMFS Datastore (already polulated with VM’s). It’s also possible to create a folder (like /vmfs/volumes/lun1/swap/srv1 and /vmfs/volumes/lun1/swap/srv2) to host multiple ESXi swap files on one VMFS Datastore. This will eliminate the need for a separate LUN for every ESXi host.