vSphere Flash Read Cache (vFRC / vFlash) and VMware Virtual SAN (vSAN) - That are the two groundbreaking features in vSphere 5.5. To use one of the features your hardware has to to fulfill a mandatory requirement - A Solid State Drive. To use a SSD with your HP Microserver you need an adapter. Most adapters or "Mounting Brackets" do not work because they are only good to fit the SSD into a 3.5" slot. They do not have the SATA Connectors at the required position. You need a special adapter for the SSD to fit into the backplane.

HP Microserver N36L

HP Microserver N40L

HP Microserver N54L

HP Microserver Gen8 G1610T

HP Microserver Gen8 G2020T

The special part of the adapter is a small circuit board with 2 connectors. There are not much products available, as the market is very small. The price varies just as the name for the "adapter":