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[Serge Hallyn <1339609@xxxxxxxxxxxxxxxxxx>]

** Also affects: linux (Ubuntu)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1339609

Title:
  md raid resync causing KVM guests overload

Status in “linux” package in Ubuntu:
  New
Status in “qemu-kvm” package in Ubuntu:
  Invalid

Bug description:
  Everytime  /usr/share/mdadm/checkarray RAID consistency check is being
  executed (started on first sunday of a month by /etc/cron.d/mdadm) on
  Ubuntu 12.04.4 KVM hypervisor, KVM guests running on the host
  (Ubuntu/Debian/Scientific linux/Windows ) start to swap, freeze,
  throwing 'BUG: soft lockup - CPU stuck for..!' errors on the consoles,
  processes are coredumping on the guests etc. KVM host starts to swap
  even it has enough memory available and every disk IO demanding
  operation/process on any guest causes whole environment is affected
  and unusable (similar situation to
  https://bugs.launchpad.net/ubuntu/+source/linux/+bug/312163).

  RAID check procedure shouldn't cause the KVM guests become unusable.

  Some of the KVM guests use either qcow2 image storage format (virtio)
  or RAW disks (LVM, virtio). All KVM guests are affected.

  Here is the system information:
  root@kvmserver:~# lsb_release -rd
  Description:    Ubuntu 12.04.4 LTS
  Release:        12.04
  root@kvmserver:~# uname -a
  Linux kvmserver 3.2.0-59-generic #90-Ubuntu SMP Tue Jan 7 22:43:51 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

  HW: Dell PowerEdge R410, 2x Intel Xeon X5650, 64GB RAM, 4x2TB SATA 6.0Gb drives in following RAID configuration:
  # cat /proc/mdstat 
  Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10] 
  md2 : active raid1 sdd3[2] sdc3[0]
        1924018648 blocks super 1.2 [2/2] [UU]
        
  md1 : active raid1 sdd2[0] sdc2[1]
        29296576 blocks [4/2] [UU__]
        
  md127 : active raid1 sde1[2] sdf1[0]
        2147481446 blocks super 1.2 [2/2] [UU]

  # free -m
               total       used       free     shared    buffers     cached
  Mem:         64419      56859       7559          0      11671       1185
  -/+ buffers/cache:      44002      20416
  Swap:        18335       5554      12781

  root@kvmserver:~# dpkg -l |egrep 'qemu-kvm|mdadm'
  ii  kvm                                  1:84+dfsg-0ubuntu16+1.2.0+dfsg+0~12.04~ppa0 dummy transitional package from kvm to qemu-kvm
  ii  mdadm                                3.2.5-1ubuntu0.3                            tool to administer Linux MD arrays (software RAID)
  ii  qemu                                 1.2.0+dfsg-0~12.04~ppa0                     dummy transitional package from qemu to qemu-kvm
  ii  qemu-kvm                             1.2.0+dfsg-0~12.04~ppa0                     Full virtualization on supported hardware

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