The distributed architecture of the software-defined storage feature in VMware VSAN enables the parameters of the storage policy to be enforced despite changes in virtual machine (VM) workload demands, or hardware or network failures. Users define storage requirements, such as performance and availability, for virtual machines on a VMware VSAN cluster. Administration of a cluster and implementation of storage policies is done in the vSphere 5.5 Web Client.
Each host in a VMware VSAN cluster requires at least one solid-state drive (SSD) which is used for caching reads and buffering writes, and at least one hard disk drive (HDD), which is used for data storage. Additional storage can be placed in the pool by adding HDDs to available ESXi hosts.