Linked Virtual Machines
and Disk Backings
In its simplest form, shared storage is
achieved through the use of delta disk backings. A delta disk backing is a
virtual disk file that sits on top of a standard virtual disk backing file.
Each time the guest operating system on a virtual machine writes to disk, the
data is written to the delta disk. Each time the guest operating system on a
virtual machine reads from disk, the virtual machine first targets the disk
block in the delta disk. If the data is not on the delta disk, the virtual
machine looks for it on the base disk.
Linked virtual machines can be created from a
snapshot or from the current running point. After you create a set of linked
virtual machines, they share the base disk backing and each virtual machine has
its own delta disk backing, as shown in
Figure 1.
Linked Virtual Machines with Shared Base Disk Backing and
Separate Delta Disk Backing
We
recommend a limit of up to eight host virtual machines accessing the same
base disk in a linked virtual machine
group. However, you can have an unlimited number of linked virtual machines
within each host virtual machine in the group.