Comment 64 for bug 1470250

I confirmed that the reproduce is repeatable. I can reproduce the bug within 30 to 60 minutes. The bug can be reproduce with the following steps:

1. Create a Virtual machine with 1 cpu and 2048M of memory.

2. Install Ubuntu on the VM. I installed 15.10(Wily).

3. Install the linux-cloud-tools package to get the VSS Snapshot daemon:
 'sudo apt-get update'
 'sudo apt-get install linux-cloud-tools'

4. Create a backup schedule for this VM to run every 30 minutes. In the advance settings I set the VSS Settings to "VSS copy Backup". I also configured the backup to backup to it's own hard disk. The machine I'm using only has two hard disks. One dedicated to Windows Server 2012 R2 and now the other for backups.

5. Download the tiobench .deb file from:
 http://packages.ubuntu.com/precise/amd64/tiobench/download

6. Install tiobench with 'sudo dpkg -i tiobench_0.3.3-5_amd64.deb'

7. Download the wrapper script that runs tiotest with the right IO pattern from bug report:
 https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1470250/+attachment/4529139/+files/run_tiotest.sh

8. Create a working directory for tiotest in the same directory where the run_tiotest.sh script was saved and will be run from:
 'mkdir tiotest-working-dir'

9.Ensure run_tiotest.sh script is executable:
 'chmod 755 run_tiotest.sh'

10. Start tiotest by running wrapper script: ./run_tiotest.sh

The bug will is reproduce when one of the backups is running. To speed things up, you could also try running "Backup once", otherwise just wait for the backups to start on their own.

The wrapper script is starting three instances of tiotest with different block sizes. My test machine has only once hard disk, so three instances of tiotest will cause the disk to be 60% to 100% utilized. This can be seen with iostat, which you can get by installing the sysstat package. If your test machine has more than once disk, more instances of tiotest may be needed in the wrapper script to increase the IO load.

Just let me know if none of the steps are clear. Now that I can reproduce the bug, I'll dig deeper and see if this is caused by a specific kernel.