Configured vs effective processor allocation
- Last UpdatedJun 04, 2025
- 2 minute read
It is recommended that you do not over-allocate resources for critical VMs.
However if you need to over-allocate processor resources due to your system requirements, Hyper-V allows you to reserve CPU cores to ensure that required resources are available when there is contention due to over-allocated resources.
We recommend that you categorize your VMs by criticality. For example, high, medium-high, medium, and low criticality and reserve certain percentages of CPU based on the criticality.
Reference guidelines for different roles are shown below.
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High: It is recommended that you reserve 100% CPU cores for these VMs.
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Medium: It is recommended that you reserver at least 50% of CPU cores for these VMs.
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Low: You may set the reservation to 0% for these VMs. The hypervisor will fully manage the processor allocation based on demand.
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Some VMs will fall between these categories, for example, the GR is considered to be medium-high criticality. Adjust the reservation accordingly.
When you reserve resources for a VM, it does not mean that the VM is always using the resources that are allocated, but rather indicates that the VM will have access to that resource when the VM demands it. For example, a node configured with 8 cores and a reserve of 100% will not be using all 8 cores unless it needs to. However, when in a CPU contention scenario, the hypervisor will ensure that the VM has access to all 8 cores.
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Note that reservation does not imply BLOCKING! Hyper-V will allow the hypervisor (1st priority) and the VMs with 0% reservation to still use available processor cycles to execute.
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VMs with a reservation are guaranteed the allocated CPUs on-demand, even in a CPU-contention scenario.
Important! Follow the Hypervisor guidelines and allow sufficient resources for the Hypervisor.
The following table shows a list of VMs in a System Platform environment and recommended minimum CPU reservation percentages.
The number of cores shown for each VM are for example only.
|
VM / Server type |
Node name |
VM criticality |
CPU cores |
Minimum recommended CPU reservation |
Effective number of CPU reserved |
|---|---|---|---|---|---|
|
Galaxy Repository / IDE |
GR |
Medium-High |
8 |
75% |
6 |
|
AOS (AppServer) |
AOS01A |
High |
16 |
100% |
16 |
|
AOS (AppServer) |
AOS01B |
High |
16 |
100% |
16 |
|
AOS (AppServer |
AOS02A |
High |
16 |
100% |
16 |
|
AOS (AppServer) |
AOS02B |
High |
16 |
100% |
16 |
|
CDP (Comms) |
COM01A |
Medium |
4 |
50% |
2 |
|
CDP (Comms) |
COM01B |
Medium |
4 |
50% |
2 |
|
Visualization |
VIS01A |
Medium |
16 |
50% |
8 |
|
Visualization |
VIS01B |
Medium |
16 |
50% |
8 |
|
Historian T1 |
HST01 |
Medium |
8 |
50% |
4 |
|
Historian T2 |
HST02 |
Medium |
8 |
50% |
4 |
|
License Server |
LC01 |
Low |
2 |
0% |
0 |
|
SMS |
SMS |
Low |
2 |
0% |
0 |
|
Total |
132 |
98 |
Notes:
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Follow the Hypervisor guidelines and make sure that there are sufficient resources left for the Hypervisor.
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Effective reserved cores should not exceed 100% of the total available processors at the hypervisor level. Depending on demand, the hypervisor may not allow you to reserve 100% of the total available processors. If effective reserved cores exceeds 100% of total available processors, some nodes will not boot.
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VMs with 100% reservation are guaranteed processing allocation on demand during CPU contention.
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Hyper-V allows the host and the VMs with 0% reservation to still use available processor cycles to execute.