@hrvojer said:
Hi all,
We have a production Windows Server 2012 R2 VM (SQL Server) that has crashed three times with the same bugcheck in xenvbd.sys. Looking for advice and for a safe download of the last 2012 R2-compatible tools.
Environment
XCP-ng 7.6.0 (yes, we know it's EOL. Right now we need a stopgap for this VM.)
Storage: LVM over FC (HPE MSA 1040), multipath
VM: Windows Server 2012 R2 (build 9600.18505), 8 vCPU, 64 GB RAM (static, dynamic min = max)
PV drivers: Citrix xenvbd.sys 8.1.0.130 (old Citrix tools)
Crashes (identical each time)
2026-06-17, 2026-09-01, 2026-10-08
BUGCHECK 0xD1 DRIVER_IRQL_NOT_LESS_OR_EQUAL (0x18, 0x2, 0x1, xenvbd+0x8795)
Write to NULL+0x18: lock xadd dword ptr [rcx+18h],eax with rcx = 0
Stack (from MEMORY.DMP):
nt!KiRetireDpcList -> nt!KiExecuteAllDpcs
-> xenvbd+0xf464 -> xenvbd+0x6f55 -> xenvbd+0xfecb -> xenvbd+0x8795
i.e. crash in a DPC, apparently in the I/O completion path.
Context
The VM ran with 16 GB RAM from 2023-09 to 2026-02 with zero crashes (no restarts at all in ~29 months).
On 2026-02-06 RAM was raised to 64 GB (SQL max server memory 14 GB -> 48 GB).
First crash 4 months later; intervals between crashes so far: 131, 76, 37 days.
Host logs at the time of the last crash: no FC/SCSI/multipath errors. The only event on this VM's VDIs was one SMGC coalesce with a clean tapdisk pause/unpause about 12 minutes before the crash.
Questions
Is this a known xenvbd bug fixed in later versions (e.g. the 9.2.1 fix "A storage error can cause Windows VMs to crash", or the grant table exhaustion fix in 9.3.1)?
A reply in the XSA-468 thread pointed to XenServer VM Tools 9.2.3 as the last version supporting 2012/2012 R2. Where can it be downloaded from an official source? downloads.xenserver.com only offers 9.6.0, and the same URL pattern for 9.2.3 returns 404.
Could the RAM increase (16 -> 64 GB) plausibly trigger this with old xenvbd (grant tables, larger I/O)? Is there a workaround that doesn't require a driver update (e.g. a host-side setting)?
We know 2012 R2 is EOL; we are looking for a safe stopgap.
Thanks!
@hrvojer Since a guest upgrade to Windows Server 2022 or 2025 is on the table, it makes the most sense to put a hypervisor upgrade to XCP-ng 8.3 LTS on the table at the exact same time.
Dropping XCP-ng 8.2.1 from your options is the right move anyway, as the 8.2 branch went completely EOL in September 2025. Jumping straight from 7.6 to 8.3 LTS (supported through late 2028) aligns perfectly with your Windows lifecycle project for a few major reasons:
Modern Kernel Compatibility: XCP-ng 7.6 does not officially support or recognize modern Windows Server 2022/2025 kernels. Attempting to force modern Windows PV tools onto a 7.6 host will lead to immediate instability.
Clean Side-by-Side Migration: XCP-ng 8.3 can safely run your legacy 2012 R2 VM. This means you can upgrade the host infrastructure first to achieve baseline stability. Once the host is on 8.3, you can spin up a fresh WS 2022/2025 VM with modern, stable PV drivers and do a clean SQL database migration, bypassing the need to troubleshoot the legacy xenvbd.sys crash entirely.
Storage & Infrastructure Breakthroughs: Moving to 8.3 unlocks SMAPIv3 and QCow2. This eliminates old VHD limits, allowing you to give your new modern Windows Server VMs massive disks up to 16 TB per image alongside the latest advancements in Xen Orchestra.
Upgrading the Windows OS while leaving the hypervisor on EOL 7.6 is essentially building a brand-new house on a crumbling foundation.
