Hyper-V’s hot-add-style memory feature is Dynamic Memory. Enable it in a virtual machine’s Settings > Memory, then configure startup, minimum and maximum RAM. To change a running VM’s allocation, raise its maximum memory; the guest can receive more memory up to that ceiling when host capacity and guest support allow.
What Hyper-V hot-add memory does
Dynamic Memory adjusts a VM’s assigned memory while it runs. Hyper-V works with Dynamic Memory components in the guest and uses memory-demand signals to determine how much to provide, including a configured buffer. The setting does not guarantee that a VM will receive its maximum: the host must have capacity, and the guest must support the feature.
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Microsoft documents two Dynamic Memory configuration changes that can be made while a VM is running: increasing maximum memory and decreasing minimum memory. In practice, increasing the maximum raises the VM’s memory ceiling without requiring a shutdown; Hyper-V can then provide additional memory as needed.
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Check compatibility before changing settings
- VM configuration version: Microsoft’s feature table lists configuration version 6.2 as the minimum for Hot Add/Remove Memory. Check the VM’s configuration version before depending on the capability: Hyper-V feature compatibility by configuration version.
- Host release: Microsoft’s Dynamic Memory overview covers Windows Server 2016, 2019, 2022 and 2025; Windows 10 and Windows 11; and Azure Local 2311.2 and later. Consult the Dynamic Memory overview for the applicable platform details.
- Guest OS: Support is guest-version-specific. Microsoft’s Ubuntu support table lists Dynamic Memory hot-add support for Ubuntu VMs on Windows Server 2016, 2019, 2022 and 2025. Verify the relevant guest operating system’s support matrix before using it in production: Supported Ubuntu virtual machines on Hyper-V.
Enable Dynamic Memory in Hyper-V Manager
- Check the VM’s current configuration. Confirm the host release, VM configuration version and guest OS support. Review the workload’s ordinary and peak memory needs before setting limits.
- Open the memory settings. In Hyper-V Manager, right-click the VM and select Settings, then choose Memory.
- Enable the feature. Select Enable Dynamic Memory. Microsoft’s walkthrough shows this checkbox in the VM’s memory settings: Microsoft Learn: Dynamic Memory for Hyper-V Virtual Machines.
- Set the memory values. Configure Startup RAM, Minimum RAM, Maximum RAM and the memory buffer. Set Startup RAM high enough for a reliable boot, Minimum RAM to the lowest safe operating level, and Maximum RAM to the ceiling the workload may need. Choose a buffer suited to how quickly its memory demand changes.
- Apply the settings and monitor the VM. Start or resume the VM as appropriate, then observe guest memory pressure and Hyper-V Dynamic Memory counters. The host must retain capacity for the management OS and virtualization services as well as its VMs.
Whether the VM must be shut down to change a particular setting depends on the Hyper-V version and guest configuration. If the setting cannot be changed in the VM’s current state, shut it down, apply the change, and start it again.
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Understand the four memory settings
| Setting | What it controls | How to choose it |
|---|---|---|
| Startup RAM | Memory assigned when the VM starts. | Allow enough for a reliable boot and startup workload. |
| Minimum RAM | The lowest amount of memory the VM retains after startup. | Use a floor that still supports the guest and its essential workload. |
| Maximum RAM | The upper limit Hyper-V can provide to the VM. | Set the intended ceiling, accounting for peak demand and host capacity. For a running VM, Microsoft documents increasing this limit as a supported Dynamic Memory change. |
| Memory buffer | A buffer Hyper-V uses when calculating memory to provide in response to demand. | Choose it according to workload variability; no universal value is established by Microsoft’s overview. |
Choose between Dynamic Memory and fixed memory
Dynamic Memory is useful when memory demand varies and greater host consolidation or in-service flexibility matters. Fixed memory keeps allocation explicit and preserves the option to use virtual NUMA. The right choice depends on workload behavior rather than a general performance guarantee.
| Consideration | Dynamic Memory | Fixed memory |
|---|---|---|
| Variable demand | Can adjust assigned memory within configured limits. | Allocation stays fixed. |
| NUMA topology | Cannot be used with Virtual NUMA; a VM with Dynamic Memory enabled effectively has one virtual NUMA node. | Preserves virtual NUMA options. |
| Host consolidation | Can improve consolidation for variable or lightly loaded VMs, subject to host capacity and guest support. | Allocates a predictable amount even when the workload is not using all of it. |
| Operational flexibility | Allows documented runtime changes to the maximum and minimum memory settings. | Does not provide Dynamic Memory’s elastic allocation behavior. |
NUMA and workload performance
Microsoft states that Virtual NUMA and Dynamic Memory cannot be used at the same time. A VM with Dynamic Memory enabled effectively has one virtual NUMA node, regardless of its virtual NUMA settings. For NUMA-aware databases or other latency-sensitive workloads, compare performance using Dynamic Memory and fixed memory before choosing a configuration. Microsoft explains the interaction in its Dynamic Memory documentation.
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If a running VM does not receive more memory
- Check the maximum: Hyper-V cannot provide memory above the VM’s configured maximum. Raise the ceiling if the workload needs more and the host can support it.
- Check host capacity: The host also needs memory for its management OS and virtualization services. A higher VM maximum does not create physical memory.
- Check the guest: Confirm that the guest OS version supports Dynamic Memory and that its Dynamic Memory components are functioning.
- Check the VM version: Confirm that its configuration version meets the documented minimum of 6.2.
- Review workload fit: If predictable NUMA topology is important, Dynamic Memory may be the wrong choice; compare against fixed memory.
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