Changing the Control Domain Memory

The Control Domain, also known as ‘Domain0’ or ‘dom0’ is a secure, privileged Linux Virtual Machine (VM) that runs the XenServer management toolstack (xapi). Besides providing XenServer management functions, the Control Domain 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 and is based on the amount of physical memory on the server. For more information, see the XenServer 7.1 CU2 Administrator’s Guide.

In Storage Read Caching and PVS-Accelerator scenarios, or when running more than 50 VMs per XenServer host, customers may wish to increase the memory allocated to dom0. On the other hand, on servers with a smaller amount of memory (less than 16GB), customers may wish to reduce the memory 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, refer to the XenServer 7.1 CU2 Administrator’s Guide.


  • Citrix recommends that you do not reduce the dom0 memory below 400MB.
  • Increasing the amount of dom0 memory will result in 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


You must 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, available memory, Control domain 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. Note that any change to the dom0 memory will cause the server to reboot.
  4. Click OK to confirm the changes and reboot the server.
Changing the Control Domain Memory