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An interesting detail from the current XenServer 9 known issues that may be particularly relevant to larger Citrix environments:
XenServer documents a Windows Server 2025 issue under CP-51655.
If many Windows Server 2025 VMs start simultaneously on the same XenServer host, some VMs may fail to start.
Why do I find this especially interesting in a Citrix context?
Because this scenario is completely normal there.
Citrix Power Management starts several workers in the morning.
An MCS catalog starts after a maintenance window.
Or PVS boots numerous targets almost simultaneously following a reboot schedule.
Initially, the symptoms may look like this:
Some of my Citrix workers will not start.
Troubleshooting will probably begin with MCS, PVS, the master image or the Delivery Controller.
But the cause may be one layer lower.
XenServer explicitly states that the issue can occur when a larger number of Windows Server 2025 VMs start simultaneously on a single host.
This also makes acceptance testing for new Server 2025 Citrix environments interesting.
A test with two or three VDAs may not be sufficient.
For XenServer 9 + Windows Server 2025, I would therefore also plan a realistic boot-storm test:
Start 5 VMs → 10 VMs → 20 VMs → 30+ VMs simultaneously.
Do not check only whether the VDAs are registered afterwards. Already at the XenServer layer, observe whether individual VM starts fail.
With Windows Server 2025 as a future multi-session platform in particular, this is a small detail with potentially significant consequences.
Known issue: CP-51655
