While it may seem trivial, there are a number of use cases for running a backup on a powered off virtual machine. This can be to increase the automation levels with VMware features such as Distributed Power Management (DPM), a subset of the Distributed Resource Scheduler (DRS) of vSphere. DPM will power down under-utilized ESX(i) servers and consolidate the workload to the remaining hosts of the DRS cluster.
While DPM does a good job of managing hosts during periods of low activity within a cluster, it doesn’t do much for virtual machines. There can be plenty of situations where virtual machines could be subject to being powered off during out-of-service hours. Shutting down Windows Servers automatically is easy enough with centralized scripts using PowerShell, shutdown.exe or even a local scheduled task. The revival task to power on the virtual machine is also an easy one-liner that can be easily automated with the Start-VM PowerCLI command, as shown below:
If a number of virtual machines are permitted to be powered off, the use case for DPM becomes more attractive. While idle virtual machines will release memory back to the host via VMware’s memory management techniques, the ultimate resource giveback is a powered off state. To be fair, when the virtual machine is powered back on, DRS and some of the memory management techniques may take time to re-arrange all of the newly added resources to the cluster.
Regardless of the reason a virtual machine is powered off, Veeam Backup and Replication can still protect the virtual machine in this state. In fact, the snapshot burden that the virtual machine, host and storage systems undergo is lessened by the fact that the redo-log files have effectively nothing to write to the source VMDK. While the virtual machine is powered off, features such as VMware’s Changed Block Tracking of each VMDK are still utilized during the backup job for optimal performance. Further, all of Veeam's restore and vPower features are available for the powered off virtual machine.
There are two important notes for backup up powered-off virtual machines, the first is that application-aware processing does not occur on a powered-off VMs and the second is that this is not a good use case for a domain controller. See this earlier blog post about what may happen for a domain controller.
As a side note, if multiple backups are run on the virtual machine while it is powered off; the subsequent backups (when using incremental mode) will be a small container only of headers because nothing has changed. In regards to excluding powered off virtual machines from a backup job, this was raised in a forum discussion and the current product only allows exclusion of templates from the backup job.
Most agent-based backup tools can't back up powered-off virtual machines. This may be an obstacle for taking DPM to the next level and setting up automated shutdown and power up operations for virtual machines, yet ensuring they are backed up. Do you perform automatic shutdown operations of virtual machines during out of service hours? Would you if you could back them up? If so, explain your environment below.