Changing the Control Domain Memory

The control domain, also known as ‘dom0’, is a secure, privileged Linux Virtual Machine (VM) that runs the XenServer management toolstack (XAPI). The control domain provides the XenServer management function. It also runs the driver stack that provides user-created VMs access to physical devices.

The amount of memory allocated to the control domain is set automatically during XenServer installation. The amount is based on the amount of physical memory on the server. For more information, see Memory usage.

You might want to increase the memory that is allocated to dom0 in the following cases: Storage Read Caching scenarios, PVS-Accelerator scenarios, or when running more than 50 VMs per XenServer server. On servers with a smaller amount of memory, you might want to reduce the memory that is allocated to dom0. The following section provides instructions to update the dom0 memory using XenCenter. For information about changing the dom0 memory using the xe CLI, see Command line interface.


  • Citrix recommends that you do not reduce the dom0 memory below 1 GiB.
  • Increasing the amount of dom0 memory causes less memory being available to VMs.
  • Customers cannot use XenCenter to reduce dom0 memory below the value that was initially set during XenServer installation.

To update the dom0 memory


Place the server in Maintenance mode before updating the dom0 memory. For more information, see Run in maintenance mode.

  1. Select the server in the Resources pane and click Memory. The Memory tab displays information about the memory currently used by the server. This information includes available memory, dom0 memory, total memory, and the percentage of the total memory used by the server.
  2. Click the hyperlink displayed next to Control domain memory. Alternatively, from the Server menu, select Control Domain Memory.
  3. Update the memory allocated to dom0 on the Control Domain Memory Settings dialog. Any change to the dom0 memory causes the server to reboot.
  4. Click OK to confirm the changes and reboot the server.
Changing the Control Domain Memory