Virtual Flash Read Cache, also called as vFlash is an feature introduced in vSphere 5.5. It increases the performance of the Virtual Machines by making use of the local SSDs. Using vFlash increases the read speed for certain workloads.
There are two main components involved in this process.
Virtual Flash Cache
Virtual Flash Device
Now that I have an 40GB SSD Storage attached to my Esxi Server, We are going to use that storage for the vSphere Read Flash Cache.
Open Web Client -> Host -> Configure -> Virtual Flash.
Click Add Capacity.
Select the local Flash Storage.
Click OK and you will see the File System configured.
Now you can configure the size of the Virtual Read Flash Cache.
I hope this helps you much in optimizing the performance of your VMs.