Installation guide

C H A P T E R 1 2 VMware ESX Server Resource Management
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Example: Web Server Consolidation
Suppose that you are using ESX Server to consolidate eight nearly-identical Web
servers running IIS on Windows 2000. Each Windows 2000 machine is configured with
512MB of memory. The native memory requirement with eight physical servers is 8 *
512MB = 4GB.
To consolidate these servers as virtual machines, 24MB is needed for the server
virtualization layer and 192MB is recommended for the service console. Each virtual
machine also requires an additional 54MB of overhead memory. An additional 6
percent should be added to account for the minimum free memory level. Assuming
no overcommitment and no benefits from memory sharing, the memory required for
virtualizing the workload is 24MB + 192MB + (1.06 * 8 * (512MB + 54MB)) = 5016MB.
The total overhead for virtualization in this case is 920MB.
If memory sharing achieves a 10 percent savings (410MB), the total memory overhead
drops to only 510MB. If memory sharing achieves a 25 percent savings (1GB), the
virtualized workload actually consumes 104MB less memory than it would on eight
physical servers.
It may also make sense to overcommit memory. For example, suppose that on
average, two of the eight Web server virtual machines are typically idle and that each
Web server virtual machine requires only 256MB to provide minimally acceptable
service. In this case, the hardware memory size can be reduced safely by an additional
2 * 256MB = 512MB. In the worst case where all virtual machines happen to be active
at the same time, the system may need to swap some virtual machine memory to
disk.
More Information
For additional background information on ESX Server memory usage, see Memory
Resource Management on page 403.