Datastores are logical container that holds specifics of each storage device and provide a uniform model for storing virtual machine files. A Datastore can be formatted with VMFS or, in the case of a NAS/NFS device, with a file system native to the storage provider. This article will introduce the types of Datastores in VMware ESXi 5.5 host.

Both VMFS and NFS Datastores can be shared across multiple ESXi hosts. Datastores can be used to store IOS image, floppy images, virtual machine files and templates.

VMFS

VMFS is a clustered file system that allows multiple ESXi hosts to read and write to the same storage device simultaneously. The size of a VMFS can be increased dynamically while virtual machines residing on the VMFS Datastore are powered on. A VMFS Datastore can support virtual disk files. A virtual disk file has a maximum of 62TB in size. It enables IT to simplify virtual machine provisioning by efficiently storing the entire machine state in a central location.

VMFS can be deployed on three kinds of SCSI-based storage devices:

• Direct-attached storage
• Fibre Channel storage
• iSCSI storage

A virtual disk stored on VMFS Datastore always appears to the virtual machine as a mounted SCSI device. The virtual disk hides the physical storage layer from the virtual machine’s operating system. For the operating system in the virtual machines, VMFS preserves the internal file system semantics. Thus the operating system running in the virtual machine sees a native file system, not VMFS. These semantics ensure correct application behavior and data integrity for applications running in virtual machines.

NFS

NFS is a file-sharing protocol that ESXi hosts use to communicate with a NAS device. NAS is a specialized storage device that connects to a network and can provide file access services to ESXi hosts.

NFS storages are treated like VMFS Datastores because they can be used to hold virtual machine files, templates and IOS images. Meanwhile, an NFS volume allows the vMotionmigration of virtual machines whose files reside on an NFS Datastore. The NFS client build into ESXi uses NFS protocol version 3 to communicate with the NAS/NFS servers.

ESXi hosts do not use the Network Lock Manager protocol, which is a standard protocol used to support the file locking of NFS-mounted files. VMware has its own locking protocol. NFS locks are implemented by creating lock files on the NFS server. Lock files are named .lck-<fileid>, where <fileid> is the value of the fileidfield. When a lock file is created, an update is periodically sent to the lock file to inform other ESXi hosts that the lock is still active. The lock file updates generate small (84-byte) WRITE requests to the NFS server.

Author: Jeffey