With vSAN the Cache Read Reservation policy for a particular VM can be set to 100% to allow all data to also exist entirely on the flash layer. The difference with Nutanix "VM Flash Mode" is, that with "VM Flash Mode" persistent data of the VM resides on Flash and is never destaged to spinning disks. In contrast, with vSANs Cache Read Reservation data exists twice: one instance on persistent magnetic disk storage and one instance within the SSD read cache.