http://www.vmware.com/files/pdf/vsphere/VMware-vSphere-Platform-Whats-New.pdf

 

VMware vSphere® 5.5 introduces new functionality to leverage flash storage devices on a VMware ESXi™ host. The vSphere Flash Infrastructure layer is part of the ESXi storage stack for managing flash storage devices that are locally connected to the server. These devices can be of multiple types (primarily PCIe flash cards and SAS/SATA SSD drives) and the vSphere Flash Infrastructure layer is used to aggregate these flash devices into a unified flash resource. You can choose whether or not to add a flash device to this unified resource, so that if some devices need to be made available to the virtual machine directly, this can be done. The flash resource created by the vSphere Flash Infrastructure layer can be used for two purposes: (1) read caching of virtual machine I/O requests (vSphere Flash Read Cache) and (2) storing the host swap file.