---
title: VMwarevSphere-VMMemoryIssues_Can_Hit_Your_VM_Performance - Codenotary
description: VMware vSphere VM Memory Issues Can Hit Your VM Performance
---

[Opvizor Blog](https://opvizor.com/blog)

# [VMwarevSphere-VMMemoryIssues\_Can\_Hit\_Your\_VM\_Performance - Codenotary](https://opvizor.com/blog/vmwarevsphere-vmmemoryissues_can_hit_your_vm_performance)

 Written by [Dennis](https://opvizor.com/blog/author/dennis) | Sep 10, 2021 9:40:25 PM

**VMware vSphere: VM Memory Issues Can Hit Your VM Performance**

Virtualization is being widely used in modern data centers and cloud  
environments due to flexibility, reliability, agility, and ease of  
management. Its hypervisor abstracts the underlying hardware and  
transparently allocates to the Virtual Machines (VMs) independent of  
their Operating Systems (OS). With help of a hypervisor, multiple  
virtual instances or VMs can be created and run on a single hardware.

[VMware vSphere](https://www.vmware.com/products/vsphere.html) offers the world’s best server virtualization  
capabilities that offer running multiple virtual instances on a single  
hardware or physical machine. Failure of hardware or poor performance of  
a physical machine affects the applications running in VMs on that  
machine, and with virtualization technology, multiple VMs running on  
that particular physical host can slow down the host and affect  
applications running on all of the VMs. Hence, performance monitoring of  
a virtual infrastructure is also very important to smoothly run and  
manage it.

The performance of any app that is running on a VM in a VMware vSphere  
infrastructure depends on many factors including:

- Server virtualization abstracts the physical resources such as CPU,  
  memory, disk, and network from the underlying hardware or hosts, and  
  shares them between hosted VMs on that hardware, and if a few VMs  
  consume a heavy amount of resources, then other VMs can’t have  
  access to those physical resources when they need it; this affects  
  the performance of the application on other VMs.
- Administrators can limit the available resources on installed VMs,  
  and not properly configured limits can congest the performance of  
  applications on those VMs.
- VMware admins sometimes over-commit physical resources to VMs on the  
  hosts, and not all VMs on these hosts may have the requirements of  
  physical resources at the same time. Over-commitment of the physical  
  resources ensures better utilization of resources, but it needs to  
  monitor the actual utilization of resources on the hosts to identify  
  where an ESXi host is resource-starved. If you haven’t identified  
  the actual utilization of resources, the performance of VMs may be  
  affected.

To improve the performance of a VM, a virtualization engineer should  
track the usage of resources by a VM over time and right-size the  
resources of VMs accordingly.

VMware vSphere contains various VM memory access resource components  
including memory ballooning and memory swapping, and in this article,  
we’ll discuss these memory access resources:

**Memory Ballooning**

[Memory ballooning](https://www.vladan.fr/what-is-vmware-memory-ballooning/) in VMware vSphere environment is a memory reclamation  
mechanism used by the ESXi (Type-1 or bare metal) to allow the ESXi host  
to reclaim unused memory from VMs, where VMs that are experiencing a  
shortage in memory can use the reclaimed memory to run an application.

Normally, the hypervisor is responsible for assigning a portion of the  
memory of the ESXi host to each installed VM on it, and the guest OS  
that runs inside a VM is unaware of available memory to the ESXi host.  
Memory ballooning makes the installed guest OS in a VM aware of the  
shortage of the ESXi host’s memory.

Whenever an ESXi host is in a situation of memory-contention and the  
VMware Tools with the ballooning driver are installed in the guest OS of  
the VM, they determine whether unused memory of any VM can be reclaimed.  
Then, the drivers inflate (balloon) the memory on an under-utilizing VM  
and prompts the ESXi host to reclaim the unused memory from that VM into  
the overall resource pool. The ESXi host then makes this additional  
physical memory available to other VMs on the ESXi host.

**How Does Memory Ballooning Work?**

Memory ballooning in VMware vSphere allows efficient utilization of  
physical memory of the ESXi host, however that comes at the cost of VM  
performance due to excessive memory ballooning on the ESXi host that  
enables the guest OS on the VM to read from the disk, and high disk I/O  
degrades the performance of a VM.

To prevent this excessive memory ballooning, VMware administrators  
should continuously track and monitor how much memory the ESXi host is  
reclaiming from the installed VMs and ensure not to grow too close to  
the set ballooning target. In the guest OS, monitoring of VMs offers  
little help in this regard, but monitoring the ballooning at host or  
hypervisor level proactively detects and controls memory excesses.

[Metrics and Logs](https://www.codenotary.com/products/metrics-and-logs/) offers to monitor the memory usage,  
memory ballooning, and memory swapping of a VMs in VMware vSphere  
environment.

[Sign up](https://www.codenotary.com/products/metrics-and-logs/) for Metrics and Logs to check your VM memory  
situation for free!

To find the above-mentioned important metrics, go to VMware Starter ->  
VMware Virtual Machine Dashboard -> Virtual Machine Memory Access  
Slowdown indicators.

**Memory Swapping**

Memory swapping occurs when the memory state of the physical host or  
ESXi host in VMware vSphere is under stress, or when reclamation  
mechanisms such as ballooning, compression, and page sharing are unable  
to keep pace with the rate of VMs memory allocation.

**How Does Memory Swapping Work in Guest OS in vSphere?**

Memory swapping occurs in VMware vSphere at two levels:

- **Memory Swapping at Guest OS Level:** When a CPU accesses a virtual
  
  > memory at the guest OS level, it is swapped into physical memory  
  > and therefore virtual memory pages become available in physical  
  > memory and are served very quickly in the virtual environment.  
  > Memory pages which are rarely used are swapped to storage, and  
  > this creates a risk of high disk I/O resulting in slow overall  
  > application performance.
- **Memory Swapping at Hypervisor-level:** At hypervisor-level, memory
  
  > pages on the VMs are swapped out to swap space, and each VM is  
  > linked to its own swap space. VMware vSphere manages the memory  
  > swapping from swap space when the guest OS accesses a memory page  
  > from the swap space. Swapping is always the last resort for a  
  > Hypervisor as data is moved from ultra-fast RAM to disk (SSD won’t  
  > help much). Ballooning is always preferred to clear memory  
  > congestion. Therefore, active memory swapping at the Hypervisor  
  > level can also be caused by missing VMware tools in the Guest OS  
  > (that perform ballooning)..

Monitoring solutions that are available in the market and focus on VM  
performance can track the poor performance of a VM but aren’t able to  
diagnose its root cause. An ideal monitoring solution for a VMware-based  
virtual environment will track memory swapping at the guest OS level and  
the hypervisor-level, while auto-correlating the metrics, and accurately  
pinpointing what is affecting the performance of a VM.

[Metrics and Logs](https://www.codenotary.com/products/metrics-and-logs/) is one of the best VMware vSphere  
monitoring solutions that runs in minutes in your virtual environment  
and immediately starts monitoring the VM memory and other important  
metrics.

**Conclusion**

To improve VM performance in a virtual environment, VMware admins should  
track the version and status of installed VMware Tools on each VM, and  
the usage of CPUs and vCPUs can also be monitored so that both the  
physical host and VMs are right sized with the right CPU resources.

[Metrics and Logs](https://www.codenotary.com/products/metrics-and-logs/) is a software that runs within  
minutes in your VMware-based virtual environment and immediately starts  
monitoring the VM memory access slowdown indicators and tracks these  
metrics over time.

[View full post](https://opvizor.com/blog/vmwarevsphere-vmmemoryissues_can_hit_your_vm_performance)

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