Satyam B. Vaghani

Virtual machine file system

The Virtual Machine File System (VMFS) is a scalable and high performance symmetric clustered file system for hosting virtual machines (VMs) on shared block storage. It implements a clustered locking protocol exclusively using storage links, and does not require network-based inter-node communication between hosts participating in a VMFS cluster. VMFS layout and IO algorithms are optimized towards providing raw device speed IO throughput to VMs. An adaptive IO mechanism masks errors on the physical fabric using contextual information from the fabric. The VMFS lock service forms the basis of VMwares clustered applications such as vMotion, Storage vMotion, Distributed Resource Scheduling, High Availability, and Fault Tolerance. Virtual machine metadata is serialized to files and VMFS provides a POSIX interface for cluster-safe virtual machine management operations. It also contains a pipelined data mover for bulk data initialization and movement. In recent years, VMFS has inspired changes to diskarray firmware and the SCSI protocol. These changes enable the file system to implement a hardware accelerated data mover and lock manager, among other things. In this paper, we present the VMFS architecture and its evolution over the years