The hardware acceleration functionality enables the ESXi host to integrate with compliant storage arrays and offload specific virtual machine and storage management operations to storage hardware. With the storage hardware assistance, your host performs these operations faster and consumes less CPU, memory, and storage fabric bandwidth.

The hardware acceleration is supported by block storage devices, Fibre Channel and iSCSI, and NAS devices.

For additional details, see the VMware knowledge base article at http://kb.vmware.com/kb/1021976.