You can aggregate local flash devices on an ESXi host into a single virtualized caching layer called virtual flash resource.
When you set up the virtual flash resource, you create a new file system, Virtual Flash File System (VFFS). VFFS is a derivative of VMFS, which is optimized for flash devices and is used to group the physical flash devices into a single caching resource pool. As a non-persistent resource, it cannot be used to store virtual machines.
After you set up the virtual flash resource, you can use it for I/O caching filters. See Filtering Virtual Machine I/O.