Knowing how much memory is available and in use on your virtual machine (VM) can help troubleshoot performance issues or determine if you need to allocate more resources. Checking your VM memory is easy to do through your hypervisor or cloud platform.
Steps to Check VM Memory
Check memory allocation
The first step is to check how much total memory is allocated to the VM.
On VMware ESXi:
- Right-click the VM in the inventory and select Edit Settings
- Look at the Memory section to see the configured RAM
On Microsoft Hyper-V:
- Open the Settings of the VM
- Look at Memory > Startup RAM to see the initial allocation
On AWS EC2:
- Select the instance in the console
- Look at the Memory field in the Description tab
On Google Cloud Platform:
- Click the VM instance
- Check the total memory allocated under Memory
View used and available memory
Once you know the total RAM, you can view how much is actively being used by applications and processes running on the VM.
- Open Task Manager > Performance tab
- Check memory sections like In Use, Available, and Shared
- Run commands like free -m or top
- Check output for total, used, free, shared, buffers, and cache memory
From a hypervisor:
- Most hypervisors show graphs or metrics for CPU and memory usage over time
- This allows you to see trends and spikes in usage
Set alerts and notifications
You can set alerts on memory usage thresholds on both the hypervisor and in the guest VM operating system to proactively notify you of potential issues.
In the guest OS:
- Use built-in performance monitor tools to set alerts
- Monitor for spikes over 85-90% sustained usage
In the hypervisor:
- Set at the VM level when usage hits 90%
- Triggers automatic alerts to your email or mobile device
- Checking VM memory is quick and easy through guest OS tools and hypervisor settings or graphs
- Monitor total allocation, active usage, available memory for performance
- Set alerts at high (85-90%) sustained memory usage to prevent issues
Knowing precisely how much memory is actively being consumed by your virtual machines allows you to properly size your environment, identify workloads that need more resources, and prevent performance degradation due to overutilization. The steps outlined above work across all major hypervisor and cloud platforms by VMware, Microsoft, AWS, GCP and more. Setting proactive alerts can save you from outages and issues down the road.
Frequently Asked Questions
- What is the best level to set a memory alert?
Set alerts around 85-90% sustained memory usage to get ahead of any potential issues.
- Can I adjust VM memory on the fly?
Yes, most hypervisors allow you to edit the allocated RAM for a running VM dynamically.
- What causes high memory usage in a VM?
Excessive applications, workloads, open files/processes will consume more RAM over time. Insufficient resources can also thrash memory.
- Is VM memory checked on Linux different than Windows?
The commands are slightly different (free, top vs. Task Manager) but provide the same memory usage statistics.
- How often should I check VM memory usage?
Review memory allocation relative to workload monthly, and monitor active VM memory usage on a weekly basis minimum.
- Can I allocate more memory without shutting down the VM?
Generally yes, as hot adding memory is a common hypervisor feature, assuming the VM hardware version supports it.
- Do VMs share memory with the host?
In some cases hypervisors will utilize host memory for shared common files, so it may show as consumed in top/free commands.
- Why would my VM show high memory but low CPU?
This can indicate a memory leak or other application issue not releasing RAM back to the system appropriately over time.
- What tool shows memory best on AWS?
The Monitoring tab in AWS console provides graphs and visuals for tracking EC2 memory consumption.
- How much memory overhead does a hypervisor use?
There is generally some percent overhead, around 5-10% on VMware ESXi and Microsoft Hyper-V for the hypervisor operations itself.
- Can I allocate more memory without a reboot?
Hot adding memory is supported in many cases, provided the VM hardware version, guest OS, and hypervisor supports the functionality.
- What is ballooning memory reclamation?
A VMware feature which can inflate or deflate VM memory based on host conditions, to dynamically distribute memory as needed.
- Is VM memory checked differently on desktop vs. server hardware?
No, the same principles and steps apply. The tools are consistent across desktop hypervisors like VMware Workstation and VMware Fusion.
- How does vMotion impact memory usage?
During a live migration event, memory pages are copied creating some brief duplication, but usage goes back to baseline after the migration completes.
- What causes my VM memory usage to spike?
New processes and services coming online, application usage changes, can all spike memory allocation which then stabilizes at a new baseline.
- How can I tell if my VM needs more memory?
Sustained high usage over 85%, system slowness, app crashes, or hypervisor alerts all indicate a potential need for more RAM allocation.
- What is the difference between memory shared, buffered, and cache?
Shared – Used by multiple processes; Buffered – For data being written to disk; Cache – Frequently accessed for performance.
- How much memory should I give my VM?
Allocate RAM based on guest OS requirements, application recommendations, and performance needs – start higher for a data-intensive server.