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VMFS (VMware ESX Server File System) is a simple, high-performance file system on physical SCSI disks and partitions, used for storing large files such as the virtual disk images for ESX Server virtual machines and, by default, the memory images of suspended virtual machines. The VMFS also stores the redo-log files for virtual machines in nonpersistent, undoable, or append disk modes. For more information on disk modes, see Creating a New Virtual Machine.

ESX Server 2.1 supports two types of file systems: VMFS version 1 (VMFS-1) or VMFS version 2 (VMFS-2). VMFS-1 is the same VMFS shipped with previous versions of ESX Server 1.x. VMFS-2 is a new VMFS released with ESX Server 2.1 and contains the following features that are not available with the older VMFS-1 file system:

• Ability to span multiple VMFS-2 partitions on the same or different SCSI disks.
• Ability for multiple ESX Servers (and the virtual machines on these servers) to access files on a VMFS-2 volume concurrently (non-clustering setup).

  VMware ESX Server 2.1 includes a new automatic per-file locking mechanism that allows these concurrent accesses without file system corruption.

• Larger file system volumes and larger files on the VMFS volumes.
• Raw disks can be mapped as VMFS files.

Note: Unlike VMFS-1, VMFS-2 is not backwardly compatible with previously released (1.x) versions of ESX Server.

A server's VMFS volumes are mounted automatically by the service console, as soon as the storage adapter drivers are loaded, and appear in the /vmfs directory.

The vmkfstools command provides additional functions that are useful when you need to create files of a particular size and when you need to import files from and export files to the service console's file system. In addition, vmkfstools is designed to work with large files, overcoming the 2GB limit of some standard file utilities.