User's Manual

be sure to follow the appropriate preparation procedure for the VM (see Section 9.9, “Preparing for Cloning a

Windows VM Using VSS” for Windows and Section 5.7, “Preparing to Clone a Linux VM” for Linux).

Note:

Templates cannot be used as normal VMs.

XenServer has two mechanisms for cloning VMs:

1. A full copy

2. Copy-on-Write (CoW)

The faster Copy-on-Write (CoW) mode only writes modified blocks to disk and is only supported for file-

backed VMs. CoW is designed to save disk space and allow fast clones, but will slightly slow down normal disk

performance. A template can be fast-cloned multiple times without slowdown.

Note:

If a template is cloned into a VM and the clone converted back into a template, disk

performance can linearly decrease depending on the number of times this has happened. In

this event, the vm-copy CLI command can be used to perform a full copy of the disks and

restore expected levels of disk performance.

Notes for Resource Pools

If you create a template on a server where all VM virtual disks are on shared Storage Repositories (SR), the

template cloning operation will be forwarded to any server in the pool that can access the shared SRs. However,

if you create the template from a VM virtual disk that only has a local SR, then the template clone operation can

only execute on the server that can access that SR.

2.2.3. Importing an Exported VM

You can create a VM by importing an existing exported VM. Like cloning, exporting and importing a VM is fast way

to create additional VMs of a certain configuration so that you can increase the speed of your deployment. You

might, for example, have a special-purpose server configuration that you use many times. Once you have set up a

VM the way you want it, you can export it, and import it later to create another copy of your specially-configured

VM. You can also use export and import to move a VM to a XenServer host that is in another resource pool.

For details and procedures on importing and exporting VMs, see Chapter 11, Importing and Exporting VMs.

2.3. XenServer Tools

XenServer Tools must be installed for each Virtual Machine (Windows and Linux) in order for the VM to have a

fully supported configuration, and to be able to use the XenServer management tools (the xe CLI or XenCenter).

A Windows VM will function without them, but performance will be significantly hampered unless the tools are

installed.

Without the tools being installed, you cannot:

• Cleanly shut down a VM

• Cleanly reboot a VM

• Suspend a VM

• Migrate a running VM (XenMotion)

• Use the checkpoint and roll back feature

• Dynamically adjust the number of vCPUs assigned to a running Linux VM- Windows VMs require a reboot for

this to take effect

For further information about XenServer Tools see Section 9.3, “XenServer Tools”