Memory Management

By Cameron Sturdevant  |  Posted 2009-03-30 Print this article Print


Memory Management

IT managers must use care to create VMotion clusters composed of Nehalem-based processors and anticipate the release of ESX 4.0 to take full advantage of the processor's new memory management features.

And these features are prodigious. The Nehalem-based processors can now handle up to 18 8GB DIMMs, for a total of 144GB of RAM per physical host.

"A general guideline is to provide 4GB of RAM per hardware thread per logical processor," said VMware's Brunner. A four-socket system with quad-core Nehalem processors could be easily accommodated in the new memory address scheme.

Aside from supporting dense VM deployments with large RAM support, Nehalem processors use another significant update dubbed VT-d (Virtualization Technology for Directed I/O) that connects dedicated DMA (direct memory access)-capable I/O resources for virtual machines.

Indeed, one of the big challenges of virtualization has been handling I/O. VT-d allows the direct assignment of a VM to a physical device. As implemented, VT-d seeks to reduce the performance overhead incurred as the hypervisor moderates state among the guest VMs.

For example, each time a network interface on the physical server processes a packet, it goes through an interrupt process in the operating system. In virtualization, the problem is that every interrupt requires that a VM exit to the VM manager and back again. Using VT-d, the VM is directly assigned to the networking device, thereby bypassing the interrupt and exit process and significantly cutting network I/O overhead.

Cameron Sturdevant Cameron Sturdevant has been with the Labs since 1997, and before that paid his IT management dues at a software publishing firm working with several Fortune 100 companies. Cameron also spent two years with a database development firm, integrating applications with mainframe legacy programs. Cameron's areas of expertise include virtual and physical IT infrastructure, cloud computing, enterprise networking and mobility, with a focus on Android in the enterprise. In addition to reviews, Cameron has covered monolithic enterprise management systems throughout their lifecycles, providing the eWEEK reader with all-important history and context. Cameron takes special care in cultivating his IT manager contacts, to ensure that his reviews and analysis are grounded in real-world concern. Cameron is a regular speaker at Ziff-Davis Enterprise online and face-to-face events. Follow Cameron on Twitter at csturdevant, or reach him by email at

Submit a Comment

Loading Comments...
Manage your Newsletters: Login   Register My Newsletters

Rocket Fuel