Frank Denneman, Senior Technical Marketing Architect, VMware
By default Storage DRS applies an Intra-VM affinity rule to each virtual machine. This default rule is commonly referred to as the VMDK affinity rule. The Intra-VM affinity rule keeps the files belonging to a virtual machine, such as the VMX file, Swap files and VMDK files together on the same datastore. If a virtual machine is migrated out of a datastore, all files will be migrated.
There is one exception to this rule and that is if an alternative swapfile location is specified. This can be done either by setting a general setting on the DRS cluster “Store the swapfile in the datastore specified by the host “ or at virtual machine level “Store in the host’s swapfile datastore”
To reduce the overhead of a virtual machine migration as much as possible Storage DRS does not move virtual machine swap files if they are stored in an alternative location, even if an Intra-VMDK affinity rule is applied.