![]() The values you're looking at here, refers to a VM and per the reference doc: When you asked earlier what is "Consumed memory", I thought you were referring to the ESX(i) host metrics. ![]() This is just a metric to show you how much of that memory is actually being actively used from the overall allocated memory.Ĭonsumed mem is 1.67GB from the host (this is what the host has allocated to the VM)Īctive guest mem 204 MB (the current amount of active guest memory in the OS) Yes, you're correct that active memory is generally lower but it does not always have to be. The metrics here is showing you how much of a particular VM is consuming from the ESX(i) host that it's being hosted on. No one likes those calls.If you're looking at the VM tab, there are 3 columns that you may be seeing: By properly provisioning VMs, you will have better performance, happier users, and less support calls at 2:00 a.m. Just because virtual resources can be over-subscribed does not mean the pool is endless. When application owners ask for new VMs, make them prove they need the resources they are requesting (if possible). The most important thing that you as a vSphere admin can do is understand the actual needs of the workloads you are hosting. This extra effort will go a long way to extend the life of your current cluster. When cloning from a template, take the time to adjust the provisioned resources to what will actually be used by the VM, otherwise resources will be wasted. One other important point is that the less memory a virtual machine has assigned, the faster it will complete a vMotion event.Ī common mistake I see often is that when new VMs are deployed from a template, they are not customized. If this is active memory, it can devastate application performance. As the hypervisor is unaware of the applications running on each workload, it will pick memory at random to page to disk if needed. Linux OSes do not have this same issue they address memory only as needed.Īccurate memory provisioning also is important in order to avoid hypervisor paging. This is why it's important to only provision as much memory as is actually needed. If it's not available, the request can cause memory reclamation to kick in and force contention. This "claims" the memory from vSphere if it is available. When a Windows server first boots, it touches all addressable memory. It's better to err on the side of caution and have too much rather than too little, but try to get as close as possible. The idea is for the delta in these two numbers to be as small as possible during peak usage. Allocated memory is the amount of physical RAM that the guest has requested from vSphere. When provisioning memory, it's important to understand active memory versus allocated memory, boot time behavior of the OS, and paging.Īctive memory is the memory that the guest OS and application actually uses. Due to the semi-persistent nature of memory, it's more complicated than CPUs to size properly. Sizing memory is a balancing act: Too much or too little can force contention. If the application is not multi-threaded and peak CPU demand is below 3000MHz, provision a single vCPU. To properly size the vCPU for a VM, look at the performance metrics of the workload. If every VM has one more vCPU than it needs, you are only getting two to three vCPUs per core. On average, you should see four to six vCPUs per physical core. However, when contention arises, an overprovisioned vCPU can cause %ReadyTime (the time a vCPU has to wait for the physical CPU) to spike and crush performance.Īdding unnecessary vCPUs can also hurt your consolidation ratio. Because of the way scheduling works, this is not usually an issue. Yet at the same time I see far more VMs with two vCPUs provisioned than with one. I would hazard a guess that at least 80% of the VMs I have come across never use more than 10% of provisioned vCPU. Let's discuss each and how it affects the proper sizing of virtual machines in a VMware vSphere environment. The three areas where I see the biggest mistakes are vCPU allocation, memory allocation, and templates. Virtualization - specifically hardware virtualization using a hypervisor - requires a change in how one thinks about resource allocation. This is because they are going about provisioning the wrong way. This is an achievable goal, but unfortunately, a large number of sysadmins are not seeing the results they expect. One of the great promises of virtualization is the ability to reclaim vast amounts of resources that stood forever idle on physical servers.
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