If you scan the bill of materials for the various Cisco UCS VSAN ReadyNodes you’ll see a line item for:

Controller Cache: Cisco 12Gbps SAS 1GB FBWC Cache module (Raid 0/1/5/6)

If you’ve followed Virtual SAN for awhile you might wonder, why would the ReadyNodes include controller cache when VMware recommends disabling controller cache when implementing Virtual SAN. Well, it turns out that the presence of the FBWC Cache module allows the queue depth of the Cisco 12G SAS Modular Raid Controller to go from the low 200’s to the advertised 895. The minimum queue depth requirement for Virtual SAN is 256 so including the FBWC Cache module allows the queue depth to increase above that minimum requirement and improve Virtual SAN performance.