How to Configure dom0 Memory in XenServer 6.1 and Later for performance
This article describes how to configure Control Domain (dom0) memory in XenServer 6.1.0 and later for better performance.
Customers running more than 50 Virtual Machines (VM) per XenServer host might wish to increase the memory allocated to dom0. The following section provides instructions to configure the dom0 memory.
To configure the dom0 memory, complete the following procedure:
1. On the XenServer host, open a local shell and log on as root.
2. Enter the following command:
/opt/xensource/libexec/xen-cmdline –set-xen dom0_mem=<nn>M,max:<nn>M
Note: <nn> represents the memory in megabytes, to be allocated to dom0. This value should be between 1024 and 4096, depending on the number of VMs that are expected to run and the total memory of the host. A higher value results in less memory being available to the VMs.
3. Reboot the XenServer host using XenCenter or reboot command on the console.
After the host is rebooted, run the command free on the console to verify the new memory settings.
Note: On smaller memory machines (less than 16GiB), some customers may want to reduce the memory allocated to dom0 lesser than the default of 752MiB.
Customers can follow the preceding instructions to reduce the dom0 memory.
However, Citrix recommends that you should not reduce the dom0 memory to lesser than 400MB.
Article by Mauro Cesar Fileto
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