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XCP-ng requirement tweaks #419

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requirements: Modernize requirements
TSnake41 Nov 26, 2025
bf30cce
requirements: Reformat maximum disk size
TSnake41 Nov 26, 2025
35dc337
requirements: Improve vCPU limit
TSnake41 Nov 26, 2025
738c3ff
requirements: Clarify NIC limit
TSnake41 Nov 26, 2025
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30 changes: 16 additions & 14 deletions docs/installation/requirements.md
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Expand Up @@ -25,20 +25,17 @@ The system requirements for XCP-ng are:
### CPUs

- One or more 64-bit x86 CPUs, minimum 1.5 GHz; 2 GHz or faster multicore CPUs are recommended.
- To run Windows VMs or recent Linux versions, an Intel VT or AMD-V 64-bit x86-based system with one or more CPUs is required.

> **Note**: For Windows VMs or newer Linux distributions, enable hardware virtualization in the BIOS. It may be disabled by default—consult your BIOS documentation for guidance.

- For VMs running supported paravirtualized Linux, a standard 64-bit x86-based system with one or more CPUs is required.
- Hardware virtualization must be enabled (Intel VT-x or AMD-V), it may be disabled by default—consult your BIOS documentation for guidance.
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@thomas-dkmt thomas-dkmt Nov 26, 2025

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Suggested change
- Hardware virtualization must be enabled (Intel VT-x or AMD-V), it may be disabled by default—consult your BIOS documentation for guidance.
:::tip
Depending on your BIOS, hardware virtualization may be disabled by default, so make sure to double-check and enable it. Refer to your BIOS documentation for guidance.

- Enabling IOMMU (Intel VT-d or AMD-Vi) is recommended

### Memory

- Minimum 2 GB, recommended 4 GB or more.
- Minimum 2 GB, recommended 8 GB or more.
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@thomas-dkmt thomas-dkmt Nov 26, 2025 •
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Suggested change
- Minimum 2 GB, recommended 8 GB or more.
- Minimum: 2 GB (Recommended: 8 GB or more).

- A fixed amount of RAM is allocated to the control domain (dom0). Optimal allocation depends on your workload.

### Disk Space

- Local storage (PATA, SATA, SCSI) with a minimum of 46 GB, recommended 70 GB or more.
- Local storage (PATA, SATA, SCSI, NVMe) with a minimum of 46 GB, recommended 70 GB or more.
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Suggested change
- Local storage (PATA, SATA, SCSI, NVMe) with a minimum of 46 GB, recommended 70 GB or more.
- Local storage (PATA, SATA, SCSI, NVMe) with a minimum of 46 GB. Recommended: 70 GB or more.

- SAN access via HBA (not software) when installing with multipath boot from SAN.

For more details, refer to the [Hardware Compatibility List (HCL)](../../installation/hardware).
Expand Down Expand Up @@ -98,7 +95,7 @@ The maximum number of supported logical processors may vary depending on the CPU
XCP-ng 8.2 is EOL. This 8.2-specific information is retained solely to assist with the transition from 8.2 to a supported release.
:::

- Up to 960 logical processors, depending on CPU support (theoretical, untested: 1024).
- Up to 960 logical processors, depending on CPU support (theoretical, untested: 2048).
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- Up to 960 logical processors, depending on CPU support (theoretical, untested: 2048).
- Up to 960 logical processors, depending on CPU support. **Note**: The theoretical, untested limit is 2,048 logical processors.

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@stormi stormi Nov 28, 2025

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Where does this number, 2048, come from? Does it apply to XCP-ng 8.3?

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@TSnake41 TSnake41 Nov 28, 2025

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https://github.com/xcp-ng-rpms/xen/blob/master/SOURCES/configure-build.patch#L370


#### XCP-ng 8.2 LTS

Expand All @@ -122,9 +119,14 @@ Below are the supported limits for virtual machines on XCP-ng.

- **Virtual CPUs (vCPUs) per VM**:
- For untrusted VMs, the security-supported limit is **32 vCPUs**.
- For trusted VMs, the tested limits are **128 vCPUs** in BIOS mode and **96 vCPUs** in UEFI mode. Developments are planned to increase these limits.
- For trusted VMs, the maximum limits are **128 vCPUs** in BIOS mode and **96 vCPUs** in UEFI mode. Developments are planned to increase these limits.
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Suggested change
- For trusted VMs, the maximum limits are **128 vCPUs** in BIOS mode and **96 vCPUs** in UEFI mode. Developments are planned to increase these limits.
- For trusted VMs, the upper limits are **128 vCPUs** in BIOS mode and **96 vCPUs** in UEFI mode. Developments are planned to increase these limits.


Guest OS support is also an important factor to consider.
Guest OS may limit the amount of usable vCPUs.

:::warning
VMs with more than 32 vCPU may cause major system-wide performance degradation under very specific circumstances. Use with caution.
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@thomas-dkmt thomas-dkmt Nov 26, 2025 •
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Is there a resource (internal or external) where the reader could know more about that? If not, no big deal but it would be nice to have

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@TSnake41 TSnake41 Nov 26, 2025

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It's a summary of what I know regarding the current "security supported" CPU limit.

XenServer docs says (even though 64 is no longer the actual limit)

Though the limit is 64, we recommend setting the limit to 32 if your VMs might not be trustworthy or if you want to prevent a potential impact on system availability

Discussions we had internally and with XenServer conclude that this is a arbitrary limit; and that guests with many CPUs can (maliciously or not) cause denial of service through abuse of some hypervisor mecanisms (that could take at the end too much time, and block multiples physical CPUs, eventually up to livelock/watchdog violation).

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@stormi stormi Nov 28, 2025

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I prefer XenServer's version (that we can't copy as is) because it insists on not trustworthy VMs yielding an increased risk

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@TSnake41 TSnake41 Nov 28, 2025

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Trustworthy suggest that trusted VMs absolutely fine, but the reality is a bit different. While malicious VMs can abuse, normal guest (with many vCPUs) can also trigger similar situations (perhaps in a less extreme way).

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@stormi stormi Nov 28, 2025

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I didn't mean to say that only untrustworthy VMs can trigger issues. I said "increased risk".

Windows VMs with more than 64 vCPUs are not supported.
:::

#### XCP-ng 8.2 LTS

Expand Down Expand Up @@ -164,14 +166,14 @@ XCP-ng 8.2 is EOL. This 8.2-specific information is retained solely to assist wi
- **Virtual Disk Images per VM (including CD-ROMs)**: Up to **241**. This is also influenced by the limits of your guest OS; refer to its documentation to ensure compatibility.
- **Virtual CD-ROM drives per VM**: **1**.
- **Maximum Virtual Disk Size**:
- **2,040 GiB** using storage drivers with the VHD format (`Local EXT`, `Local LVM`, `NFS`, `LVM over iSCSI`, `XOSTOR`, etc.).
- **2 TiB** using storage drivers with the VHD format (`Local EXT`, `Local LVM`, `NFS`, `LVM over iSCSI`, `XOSTOR`, etc.).
- Nearly unlimited when using the `raw` storage driver or disk pass-through to the VM (note: snapshots and live migration are not supported in these cases).
- New storage drivers are under active development to overcome the **2,040 GiB** VHD limit while retaining features like snapshots and live migration.
- New storage drivers are under active development to overcome the **2 TiB** VHD limit while retaining features like snapshots and live migration.

### Networking

- **Virtual Network Interface Controllers (NICs) per VM**: Up to **7**.
Note: Some guest operating systems may have stricter limits, or you may need to install XCP-ng Guest Tools to reach this maximum.
Use of paravirtualized devices is recommended, support depends on guest operating system and whether or not XCP-ng Guest Tools are installed.
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@thomas-dkmt thomas-dkmt Nov 26, 2025 •
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Suggested change
Use of paravirtualized devices is recommended, support depends on guest operating system and whether or not XCP-ng Guest Tools are installed.
We recommend using paravirtualized devices. Support depends on guest operating system and whether or not XCP-ng Guest Tools are installed.

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@TSnake41 TSnake41 Nov 26, 2025

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not sure paravirtualized resources is better; but something in between like paravirtualized interfaces could be better ?

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Paravirtualized devices is OK, I'm changing my suggestion


### Other

Expand All @@ -183,7 +185,7 @@ A resource pool is a collection of one or more servers (up to 64), which can be

### Hardware Requirements

- All servers must have compatible CPUs (same vendor — Intel or AMD). To run HVM VMs, CPUs must support virtualization.
- All servers must have compatible CPUs (same vendor — Intel or AMD).
Comment on lines -186 to +188
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@ydirson ydirson Nov 26, 2025

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Shouldn't we leave out the "To run HVM VMs," part?

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@TSnake41 TSnake41 Nov 26, 2025

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"virtualization" is already a hard requirement for XCP-ng 8.3, so this statement is redundant


### Additional Pool Requirements

Expand Down