Known Issues
This article contains advisories and minor issues in the XenServer 9 release and any workarounds that you can apply.
General
- When attempting to use the serial console to connect to a XenServer® host, the serial console might refuse to accept keyboard input. If you wait until after the console refreshes twice, the console then accepts keyboard input.(CA-311613)
Guests
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When defining the vCPU topology for a new VM, ensure that the number of cores per socket is set to a power of two (1, 2, 4, 8, and so on). If this value is not set to a power of two, some of your cores are not utilized by the VM, topology information shown inside the VM operating system might be incorrect, and other unexpected behaviors might be observed.(XSI-1766)
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If your VM enters sleep mode, your mouse might become unresponsive although your keyboard remains functional. Rebooting the VM or disabling and enabling the USB controller through Device Manager restores mouse functionality.(CA-399746)
RPU (Rolling Pool Upgrade)
- Attempting to upgrade a host to XenServer 9 with the install media located on an NFS target may fail with the error
ERR_REPO_QUERY_PROVIDES. This issue is expected to be resolved in a future XenServer 8.4 update. (CA-423692)
Performance
- NUMA node drift: when VMs fully use all CPUs on the host, then the hypervisor may run some vCPUs on NUMA nodes far from where the VM’s memory is located, causing a performance degradation. Use the
NUMA non-affine vCPUsRRD (XenCenter Performance Graph) to monitor whether you are affected by this, and try to leave at least 1 CPU idle to recover. (XSI-1573)
T4 vGPU VMs display black screen with NVIDIA host driver 580.105.06
Windows VMs with NVIDIA T4 vGPU configuration display a black screen on both console and RDP after upgrading the XenServer host to NVIDIA vGPU Manager driver version 580.105.06. This issue affects all tested guest driver versions and appears to be related to GPU memory allocation failures in the host driver.
Workaround
Downgrade the NVIDIA host and VM drivers to version 535.274.03.
Windows guests
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For domain-joined Windows 10 VMs (1903 and later) with FireEye Agent installed, repeated successful RDP connections can cause the VM to freeze with 100% CPU usage in
ntoskrnl.exe. Perform a hard reboot on the VM to recover from this state. (CA-323760) -
When you create a UEFI VM, the Windows installation requires a key press to start. If you do not press a key during the required period, the VM console switches to the UEFI shell.
To work around this issue, you can restart the installation process in one of the following ways:
- In the UEFI console, type the following commands:
EFI:
EFI\BOOT\BOOTX64
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- Reboot the VM
When the installation process restarts, watch the VM console for the installation prompt. When the prompt appears, press any key.(CA-333694)
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If you boot a large number of Windows Server 2025 VMs on a single host at the same time, some might fail to start.(CP-51655)
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If an imported Windows VM already has XenServer VM Tools installed, attempting to install the same version of the tools again during the import process fails.(CA-413698)
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If you import a Windows Server VM with more than 4 disks, some of the disks show as offline.(CA-414047)
For details on the latest XenServer VM Tools for Windows release, see What’s new.
Linux guests
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You cannot use the Dynamic Memory Control (DMC) feature on Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Rocky Linux 8, Rocky Linux 9, or CentOS Stream 9 VMs as these operating systems do not support memory ballooning with the Xen® hypervisor.(CA-378797)
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On some Linux VMs, especially busy systems with outstanding disk I/O, attempts to suspend or live migrate the VM might fail. To work around this issue, try increasing the value of
/sys/power/pm_freeze_timeout, for example, to 300000. If this work-around is not successful, you can upgrade the Linux kernel of the VM to the latest version.(CP-41455) -
Linux VMs without the guest agent installed cannot be cleanly shut down, rebooted, suspended, or migrated, after having previously been migrated or resumed from suspend. Installing the guest agent restores the functionality.(CA-423819)
Storage
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You cannot run more than 200 PVS-Accelerator-enabled VMs on a XenServer host.(CP-39386)
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When read caching is enabled, it may be slower to read from the parent snapshot than from the leaf. To work around this issue, allocate more memory to dom0.(CP-32853)
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Sometimes, when the most recent snapshot for a VM is deleted, it is not possible to completely merge the data from the active VM disk into its parent device. Often, this is caused by the VM being active and writing data to the disk faster than the merge process can merge it. As a result, the VM might use more storage space than is usually necessary due to having two virtual disks in a delta parent/child arrangement. This issue can have more impact on LVM-based SR types as the VMs active write disk is fully provisioned. To allow for the data merge process to complete, either
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Temporarily reduce the storage I/O rate that the VM is producing.
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Shut down the VM.
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Then rescan the SR on which the VM’s disks are stored.(XSI-1922)
Third-party
- A limitation in recent SSH clients means that SSH does not work for user names that contain any of the following characters:
{}[]|&. Ensure that your user names and Active Directory server names do not contain any of these characters.
XenCenter
For information about known and fixed issues in XenCenter, see XenCenter What’s New.