Hyper-V Gains Dynamic Memory

Dynamic memory, a new feature added to Windows Server that allows its Hyper-V hypervisor to change the amount of memory allocated to a running virtual machine (VM), will ship with Windows Server 2008 R2 SP1. Using dynamic memory, customers may be able to run more VMs on a physical server, reducing costs and erasing one of VMware’s key advantages, its dynamic memory allocation. In order to use dynamic memory, however, both the host computer and the VMs need upgraded OS components.

Dynamic Memory

Dynamic memory pools physical memory in a Windows Server 2008 R2 SP1 server so that memory in the pool can be distributed as needed to running VMs, based on their workload memory requirements and the priority of the VM relative to other running VMs.

Dynamic memory is particularly useful because it is difficult to anticipate exactly how much memory a VM might need, and allocating enough memory to handle peak workloads can result in wasted memory. Typically, administrators guess high or add additional memory in order to provide a cushion to handle temporary spikes in the workload. As a result, a large amount of memory could be allocated but never used, which reduces the number of VMs that can run on a host. Dynamic memory, in contrast, enables an administrator to configure a new VM so it will have enough memory if it encounters heavy workloads. It also means an administrator can put more VMs on a physical server by allocating enough memory to get the VMs started and running a normal workload, allowing the VMs to take memory from the pool of free memory if their workloads increase. VM uptime should also improve if a VM does not have to be stopped to adjust memory.