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When calculating the memory footprint of a Xen host there are two components that must be taken into consideration. First there is the memory consumed by the Xen hypervisor itself; then there is the memory consumed by the host's control domain. The control domain is a privileged VM that provides low-level services to other VMs, such as providing access to physical devices. It also runs the management tool stack. On a XenServer host, the Xen hypervisor (and its associated system tools) occupies approximately 128 MB of RAM. Calculating the memory consumed by the control domain is more complicated, since this value depends on the amount of physical RAM in the particular host. The memory used by the control domain is always at least 200MB, and is never more than 752MB; within that range it is scaled as a linear function of total host RAM. For hosts with up to 3.5GB of physical RAM, the control domain usage remains at 200MB; on a 5GB host the control domain will use 228MB; on a 16GB host the control domain consumes 454MB; and on hosts with 32GB or more the control domain consumes 752MB. The default memory scaling algorithm is designed to be sufficient for using normal guest operating systems with over 256MB of RAM and 2-4 virtual disks. If you have more specialized requirements (e.g. a large number of VMs with 64MB of RAM each, and 7 virtual disks each), you may need to tweak the amount of memory reserved for the control domain. This is an advanced operation, and you may wish to contact XenSource Support before doing this. When you have installed your XenServer host, log into the host console and type in cat /proc/meminfo. The value of The memory reservation algorithm is based on the total amount of RAM in your XenServer host, and is calculated by:126 + (G * T) where The value of the memory gradient can be increased by altering the value in | |||||||||||||
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