Performance By Design

Let’s look at an example of what happens when Hyper-V machine memory is over-committed and the Dynamic Memory Balancer attempts to adjust to that condition. The scenario begins with five Windows guest machines running with the following dynamic memory settings: Minimum Maximum WIN81TEST1 2 GB 6 GB WIN81TEST2 2 GB 6 GB WIN81TEST3 512 MB 6 GB WIN81TEST4 512 MB 6 GB WIN81TEST5 512 MB 8 GB In the scenario, four of the five guest machines are doing actual work. Only guest machine 5 is active, as illustrated in the screen shot of the Hyper-V Manager console, shown in Figure 17. The Hyper-V Host used in the test contains 12 GB of RAM. The remaining guest machines are idle initially, which allows Hyper-V to reduce the amount of machine memory allocated to guests 3-4 to near their minimum values, using the ballooning technique we discussed.  Figure 17. The Hyper-V...

In the l ast post in this series, I began discussing the Hyper-V dynamic memory, which is one of the main features that differentiates Microsoft's virtualization technology from VMware. This post continues to look at dynamic memory in Hyper-V. Dynamic memory options There are several more dynamic memory parameters that can also be set, including the amount of Guest Physical memory to grant the guest machine at start-up, a provision for a machine memory buffer for Hyper-V to maintain as a reserve, and a weighting factor for prioritizing the various guest machines in case demand for machine memory begins to exceed the supply. These guest machine settings are illustrated in the screen shot shown in Figure 11.  Figure 11. Dynamic memory settings for a guest machine. The minimum Minimum RAM setting is 32 MB.  Consider the dynamic memory configuration of the guest machine shown in Figure 11. The amount of RAM requested at startup in this example is 2 GB. If that amount...

Dynamic memory. The Hyper-V hypervisor can adjust machine memory grants to guest machines up or down dynamically, a feature that is called dynamic memory . Dynamic memory refers to adjustments in the size of the Guest Physical address space that the hypervisor grants to a guest machine running inside a child partition. When dynamic memory is configured for a guest machine, Hyper-V can give a partition more physical memory to use or remove guest physical memory from a guest machine that doesn’t require it, ignoring for a moment the relative memory priority of the guests. With the dynamic memory feature of Hyper-V, you can pack significantly more virtual machines into the memory footprint of the VM host machine, although you still must be careful not to pack in too many guest machines and create a memory bottleneck that can impact all the guest machines that are resident on the Hyper-V Host.  When dynamic memory is enabled for a child partition, you set minimum and maximum Gu...