VMware vSphere VMFS
Physical file systems usually allow only one host to have read-write access to the same file at a given time. By contrast, VMware vSphere VMFS enables a distributed storage architecture that allows multiple ESXi hosts concurrent read and write access to the same shared storage resources. VMFS is optimized for a virtualized environment and offers a high-performance cluster file system designed specifically for virtual machines. It uses distributed journaling of its file system meta data changes to allow fast and resilient recovery in the event of a hardware failure. VMFS is also the foundation for distributed infrastructure services, such as live migration of virtual machines and virtual machine files, dynamically balance workloads across available compute resources, automated restart of virtual machines and fault tolerance.
VMFS provides an interface to storage resources so that several storage protocols (Fibre Channel, Fibre Channel over Ethernet, NAS, iSCSI) can be used to access datastores on which virtual machines can reside. Dynamic growth of VMFS datastores through aggregation of storage resources and dynamic expansion of a VMFS datastore enables you to increase a shared storage resource pool with no downtime. In addition, you have a means for mounting a point in time copy of a datastore.