[Qemu-devel] [Bug 1201447] Re: Blue screen when disk uses cache='writeback'

[Thomas Huth]

** Project changed: qemu => qemu (Ubuntu)

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https://bugs.launchpad.net/bugs/1201447

Title:
  Blue screen when disk uses cache='writeback'

Status in qemu package in Ubuntu:
  New

Bug description:
  I am running Windows 2008R2 as KVM guest on Ubuntu 12.04 hypervisor. Disk 
controller and network card are virtio devices with drivers from 
https://launchpad.net/kvm-guest-drivers-windows/+download 
(virtio-win-drivers-20120712-1.iso).
  Everything worked fine until I changed disk controller cache from the default 
(writethrough) to writeback. This introduced occasional blue screens. I noticed 
that they are linked to high disk IO. For example restoring over 1GB of backup 
files will results in a blue screen on around 4 out of 5 attempts. Also Windows 
update crashes the system sometimes. When idle the system will run fine for 
hours or sometimes even days.
  After removing cache='writeback' from the config everything came back to 
normal.

  qemu-kvm:
    Installed: 1.0+noroms-0ubuntu14.8
    Candidate: 1.0+noroms-0ubuntu14.8
    Version table:
   *** 1.0+noroms-0ubuntu14.8 0
          500 http://archive.ubuntu.com/ubuntu/ precise-updates/main amd64 
Packages
          100 /var/lib/dpkg/status
       1.0+noroms-0ubuntu14.7 0
          500 http://security.ubuntu.com/ubuntu/ precise-security/main amd64 
Packages
       1.0+noroms-0ubuntu13 0
          500 http://archive.ubuntu.com/ubuntu/ precise/main amd64 Packages

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