linked clones

A linked clone is a copy of a virtual machine (VM) that shares virtual disks with its parent VM. The term is most often associated with VMware.

In a virtual desktop infrastructure (VDI), a linked clone contains all the files available on a parent VM at the time of a snapshot. Although the linked clone must always have access to the parent VM or it will shut down, changes to the parent VM's virtual disks do not affect the linked clone -- or vice versa. Instead, to preserve disk capacity, changes are stored in a delta disk on a per-VM basis.

If an administrator wants to update a parent's VM and have those changes reflected on the children, the administrators needs to perform a recompose. Desktop recomposition simultaneously updates all the linked clone desktops anchored to a parent virtual machine so the linked clones point to the right base disk. The net effect is all the changes accrued in the delta disk are lost, and users get a brand new virtual desktop. To do this, however, end users have to log off their desktops and then log back on when the new desktop is ready. 

For linked clones to be possible, administrators must install the VMware View Composer Service on their vCenter servers.

See also: thin provisioning, differencing disks

This was last updated in October 2013

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