Skip to content

XCP-ng requirement tweaks #419

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
TSnake41 wants to merge 4 commits into
base: master
Choose a base branch
from
Open

XCP-ng requirement tweaks #419

Changes from all commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
c3d4bde
requirements: Modernize requirements
TSnake41 Nov 26, 2025
59f42c9
requirements: Reformat maximum disk size
TSnake41 Nov 26, 2025
91ec7dd
requirements: Improve vCPU limit
TSnake41 Nov 26, 2025
54277e1
requirements: Clarify NIC limit
TSnake41 Nov 26, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
32 changes: 19 additions & 13 deletions docs/installation/requirements.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -25,20 +25,22 @@ 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.
- Hardware virtualization must be enabled (Intel VT-x or AMD-V).
- Since XCP-ng 8.3, CPU must support SLAT (Intel EPT or AMD RVI/NPT).
Copy link
Copy Markdown
Member

@stormi stormi Jan 14, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Suggested change
- Since XCP-ng 8.3, CPU must support SLAT (Intel EPT or AMD RVI/NPT).
- Since XCP-ng 8.3, CPUs must support SLAT (Intel EPT or AMD RVI/NPT).

- For stability and proper support of some features, enabling IOMMU (Intel VT-d or AMD-Vi) is recommended.

> **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.
:::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.
:::

### Memory

- Minimum 2 GB, recommended 4 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.
- 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 +100,7 @@ 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. **Note**: The theoretical, untested limit is 2,048 logical processors.

#### XCP-ng 8.2 LTS

Expand All @@ -122,9 +124,13 @@ 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 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.
Copy link
Copy Markdown
Collaborator

@thomas-dkmt thomas-dkmt Nov 26, 2025 •
edited
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

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

Copy link
Copy Markdown
Member Author

@TSnake41 TSnake41 Nov 26, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

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).

Copy link
Copy Markdown
Member

@stormi stormi Nov 28, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

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

Copy link
Copy Markdown
Member Author

@TSnake41 TSnake41 Nov 28, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

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).

Copy link
Copy Markdown
Member

@stormi stormi Nov 28, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

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

Copy link
Copy Markdown
Member

@stormi stormi Jan 14, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Can you try another wording?

:::

#### XCP-ng 8.2 LTS

Expand Down Expand Up @@ -164,14 +170,14 @@ 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**.
Copy link
Copy Markdown
Member

@stormi stormi Jan 14, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Since the last batch of updates, we support up to 16. Let's update.

Suggested change
- **Virtual Network Interface Controllers (NICs) per VM**: Up to **7**.
- **Virtual Network Interface Controllers (NICs) per VM**: Up to **16**.

Note: Some guest operating systems may have stricter limits, or you may need to install XCP-ng Guest Tools to reach this maximum.
We recommend using paravirtualized devices is recommended. Support depends on guest operating system and whether or not XCP-ng Guest Tools are installed.
Copy link
Copy Markdown
Member

@stormi stormi Jan 14, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I actually prefer the former version. What's your intent with this change?


### Other

Expand All @@ -183,7 +189,7 @@ 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 thread
stormi marked this conversation as resolved.

### Additional Pool Requirements

Expand Down