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.

thick – Space required for the virtual disk is allocated during creation. This type of formatting doesn’t zero out any old data that might be present on this allocated space. A non-root user is not allowed to create this format.

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 – Virtual compatibility mode raw disk mapping.

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

raw – Raw device.

2gbsparse – A sparse disk with 2GB maximum extent size. You can use disks in this format with other VMware products, however, you cannot power on sparse disk on an ESX host unless you first re-import the disk with vmkfstools in a compatible format, such as thick or thin.

monosparse – A monolithic sparse disk. You can use disks in this format with other VMware products.

monoflat – A monolithic flat disk. You can use disks in this format with other VMware products.

Note

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

Thick, zeroedthick and thin usually mean the same because the NFS server and not the ESX host decides the allocation policy. The default allocation policy on most NFS servers is thin.