To store virtual disks, ESXi uses datastores, which are logical containers that hide specifics of physical storage from virtual machines and provide a uniform model for storing virtual machine files. Datastores that you deploy on block storage devices use the vSphere VMFS format, a special high-performance file system format that is optimized for storing virtual machines.

Several versions of the VMFS file system have been released since its introduction. The following table shows host-to-VMFS version relationships.

Table 1. Host access to VMFS version

VMFS

ESX/ESXi 3.x host

ESX/ESXi 4.x host

ESXi 5.x host

VMFS2

RO

RO

N

VMFS3

RW

RW

RW

VMFS5

N

N

RW

  • RW: Complete read and write support. You can create and power on virtual machines.

  • RO: Read only support. You cannot create or power on virtual machines.

  • N: No access. ESXi 5.x does not support VMFS2. If your datastore was formatted with VMFS2, first upgrade the datastore to VMFS3 using legacy hosts and the vSphere Client.

Use the vSphere Web Client to set up a VMFS datastore in advance on a block-based storage device that your ESXi host discovers. A VMFS datastore can be extended to span several physical storage extents, including SAN LUNs and local storage. This feature allows you to pool storage and gives you flexibility in creating the datastore necessary for your virtual machines.

You can increase the capacity of a datastore while virtual machines are running on the datastore. This ability lets you add new space to your VMFS datastores as your virtual machine requires it. VMFS is designed for concurrent access from multiple physical machines and enforces the appropriate access controls on virtual machine files.