kantver - Fotolia
Virtualization has changed the way server resources are distributed and used in enterprise workloads. The days when a server hosted a single physical application are long gone, and virtual machines can utilize almost all of a server's computing resources. Server administrators must ensure that each virtual machine receives adequate processor, memory, storage and network resources. But workload performance and stability are often most affected by memory, and memory shortages or performance issues can have a profound impact on VMs -- even the entire server.
Modern computers treat memory as a "virtual" resource even when hypervisors are not used. When a program tries to access memory, the computer must translate the virtual address to a physical address. This is handled through a page table or translation lookaside buffer.
Virtualization complicates this process. When a hypervisor adds a virtualization layer to the computer, this translation has to be performed twice; first to translate the VM's virtualized address to the host computer's virtual address scheme, and second to translate the host computer's virtual address scheme to its physical, or machine, address.
This second-level address translation (SLAT) was normally handled in virtual machine manager software -- part of the hypervisor, such as VMware's ESXi -- but the need for additional memory address translation cycles could slow VM performance anytime address translation is needed. Processor manufacturers like Intel and AMD realized that VM performance could be improved by handling second-level address translation directly through the processor.
Intel's implementation of second-level address translation is called extended page tables and is implemented in Westmere-EX core Xeon processors for servers -- with some desktop and mobile versions also. These include products in Intel's E7-88xx, E7-48xx and E7-28xx families as well as E56xx, L56xx and X56xx products. AMD implements SLAT through rapid virtualization indexing which is also dubbed nested page tables. Rapid virtualization indexing appeared in Barcelona core Opteron processors.
Remember that some hypervisors, such as Hyper-V in Windows 8, abandon software-based memory virtualization and require hardware-assisted second-level address translation for normal operation. Be sure to check for system requirements before deploying or upgrading hypervisors to ensure the new hypervisor will function properly on a non- second-level address translation hardware platform. If not, a hardware upgrade will be required to provide a SLAT-capable processor.
Monitoring VMware memory and CPU use
An overview of VMware ESXi security features
Hypervisor memory paging techniques and capabilities
Dig Deeper on Server consolidation and improved resource utilization
Related Q&A from Stephen J. Bigelow
Embedded systems and hypervisors go hand in hand. By understanding both, admins can maximize system benefits such as multiple OS support and legacy ... Continue Reading
Application load balancers and API gateways both manage network traffic, but in their own ways. Learn the differences between them and how to use ... Continue Reading
Developers don't have a lot of free time. Code reuse helps dev teams focus on the most value aspects of a project, so ensure everyone knows how to ... Continue Reading
Have a question for an expert?
Please add a title for your question
Get answers from a TechTarget expert on whatever's puzzling you.