Understanding Memory Management in VMware vSphere 5

VMware (in ESXi) has a popular, though complex to learn, set of memory management technologies. This paper describes what is what and what is new in vSphere 5 ( Swap to SSD).

VMware ESXi™, a crucial component of VMware vSphere 5.0, is a hypervisor designed to efficiently manage hardware resources including CPU, memory, storage, and network among multiple, concurrent virtual machines. This paper describes the basic memory management concepts in ESXi, the configuration options available, and provides results to show the performance impact of these options. The focus of this paper is in presenting the fundamental concepts of these options. ESXi uses high-level resource management policies to compute a target memory allocation for each virtual machine (VM) based on the current system load and parameter settings for the virtual machine (shares, reservation, and limit2). The computed target allocation is used to guide the dynamic adjustment of the memory allocation for each virtual machine. In the cases where host memory is overcommitted, the target allocations are still achieved by invoking several lower-level mechanisms to reclaim memory from virtual machines. This paper assumes a pure virtualization environment in which the guest operating system running inside the virtual machine is not modified to facilitate virtualization (often referred to as paravirtualization). Knowledge of ESXi architecture will help you understand the concepts presented in this paper.


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