When you create or clone a virtual disk, you can use the -d --diskformat suboption to specify the format for the disk.

Choose from the following formats:

  • zeroedthick (default) – Space required for the virtual disk is allocated during creation. Any data remaining on the physical device is not erased during creation, but is zeroed out on demand at a later time on first write from the virtual machine. The virtual machine does not read stale data from disk.

  • eagerzeroedthick – Space required for the virtual disk is allocated at creation time. In contrast to zeroedthick format, the data remaining on the physical device is zeroed out during creation. It might take much longer to create disks in this format than to create other types of disks.

  • thin – Thin-provisioned virtual disk. Unlike with the thick format, space required for the virtual disk is not allocated during creation, but is supplied, zeroed out, on demand at a later time.

  • rdm:device – Virtual compatibility mode raw disk mapping.

  • rdmp:device – Physical compatibility mode (pass-through) raw disk mapping.

  • 2gbsparse – A sparse disk with 2GB maximum extent size. You can use disks in this format with hosted VMware products, such as VMware Fusion, Player, Server, or Workstation. However, you cannot power on sparse disk on an ESXi host unless you first re-import the disk with vmkfstools in a compatible format, such as thick or thin.

    See Migrate Virtual Machines Between Different VMware Products.

NFS Disk Formats

The only disk formats you can use for NFS are thin, thick, zeroedthick and 2gbsparse.

Thick, zeroedthick and thin formats usually behave the same because the NFS server and not the ESXi host determines the allocation policy. The default allocation policy on most NFS servers is thin. However, on NFS servers that support Storage APIs - Array Integration, you can create virtual disks in zeroedthick format. The reserve space operation enables NFS servers to allocate and guarantee space.

For more information on array integration APIs, see Storage Hardware Acceleration.