Recommended Reading : Performance of vSphere Flash Read Cache in VMware vSphere 5.5

In VMware vSphere 5.5 a new approach to leverage flash storage devices was introduced. The vSphere Flash infrastructure layer is part of the ESXi storage stack allows management of flash storage devices connect to the ESXi host server. Typically these devices can be PCIe flash cards or SAS/SATA SSD drives.  The flash resource created by the vSphere Flash infrastructure layer can be used for two purposes : read caching of virtual machine I/O requests (vSphere Flash Read Cache) and storing the host swap file.

VMware

This whitepaper offers some performance best practices and look at a set performance benchmarks.