Before some days CentOS team released a new version with number 6.6. After some upgrades and lab tests in the infrastructure I found some problems with the backing up procedure from the DPM and generally with the VSS.
To be more specific when you try to take a backup from a CentOS 6.6 upgraded image from CentOS 6.5 with Hyper-V Backup Essentials installed (the module/package which was till 6.5 responsible for the VSS backup on Linux VMs) you are getting freeze the VM (hang) with kernel panic errors on the /var/log/messages file. So the only thing you can do is to hard reset your VM in order to be operational. The thing is that after the hard reset of your VM you will still can't take backup with VSS enabled. The one way to don't mess with this thing is to go on your Hyper-V Manager -> Virtual Machine settings and uncheck the Backup on the Integration Services configuration. The second way to avoid all this thing and use operational the VSS, please follow the below instructions:
1. You have to remove your integration services so you can install again the new released package for CentOS 6.6 (hyperv-daemons) which includes the Online backup ability without any problem
rpm -e microsoft-hyper-v kmod-microsoft-hyper-v
When uninstall complete please reboot your VM.
2. After the reboot please login on your VM and install the hyperv-daemons package (if you are not root run it with sudo in front of the command below)
yum install hyperv-daemons
When install complete please reboot your VM.
Even after the above instructions completed and the VM is working fine, when you try to backup your VM you will get some errors on your remote console of hang_task_timeout_secs and inside the /var/log/messages file that the Hyper-V VSS: VSS: freeze of /boot: Permission denied. After a contact with Microsoft and some other on Technet the workaround is below. These problems occurs because of the SELINUX is not disable and be more specific it doesn't allow the hyper-v vss daemon to run. To workaround it please do the following:
1. Disable SELINUX
1.1 vi /etc/selinux/config1.2 disable SELINUX1.3 press ESC1.4 :wq1.5 reboot
2. If you are having strictly policy and for some reason you are using the SELINUX firewall module, run the following command in order to give rights on the hyper-v vss daemon to run on your CentOS
semanage permissive -a hypervvssd_t
If you get an error "command not found" is because you have to install the python policy core utilities that SELINUX uses. Run the following command in order to install them:
yum install policycoreutils-python
These things above have been tested on Windows Server Hyper-V 2012 R2 and DPM 2012 R2 UR3 and works without any problem (for now) Please, bofore do anything on your production Virtual Machines please test it on your infrastructure too because some things might not be the same or not fitting with the guide above. If you have any additional informations please comment.
Have a nice day.