Knowledge Base

The memory management system in ESX Server allows you to control a number of parameters that affect the amount of memory available to each virtual machine. Here are a few things you should check.

• Be sure you have installed VMware Tools in all your virtual machines. The VMware Tools package includes a component that helps reclaim unused memory so you can run more virtual machines at the same time.
• Allow one virtual machine to finish booting its guest operating system before starting the next one. This ensures that the memory management component of VMware Tools is running. You may need to wait a few additional seconds to give the memory management system time to reclaim unused memory from running virtual machines.
• Adjust the memory settings for all running virtual machines. Pay particular attention to the minimum memory set for all machines. You need at least enough physical memory on the server to accommodate the ESX Server virtualization layer (approximately 24MB), the console operating system, memory overhead for all running virtual machines and the minimum memory set for all running virtual machines.

  When you set memory for the console operating system, follow these guidelines:

  • 128MB for <= 4 virtual machines
  • 192MB for <= 8 virtual machines
  • 272MB for <= 16 virtual machines
  • 384MB for <= 32 virtual machines
  • 512MB for > 32 virtual machines

    Plan for each virtual machine's overhead memory according to the following guidelines: A virtual machine configured with less than 1GB of memory requires 32MB of overhead memory. Larger virtual machines require an additional 4MB of overhead memory per additional gigabyte of configured main memory. For example, a virtual machine with a configured maximum memory size of 2GB requires 36MB of overhead memory.

    You can adjust the minimum memory setting for a virtual machine using the VMware Management Interface - in the RAM section of the Resource Editor page. On the server's Overview page, click Manage Resources. The Resource Monitor page appears. Click Edit Resources under the name of the virtual machine for which you want to change the setting. Enter the desired setting, then click Save Changes.

See the section Sizing Memory on the Server in your ESX Server manual for more detailed information.