When I read recently that Virtual Server 2005 R2 SP1 will support Volume Shadow Copy Service (VSS) I was quite excited. This means that you can backup a running virtual machine without shutdowns. Some weeks ago I decided against Virtual Server 2005 and for VMware Server. However, VSS support is a killer feature in my view. Today, I tried to backup a running virtual Windows Server Virtual Server 2005 R2 SP1 Beta2 using Symantec Backup Exec 10d.
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Of course you can backup a virtual server like any other server by installing the backup agent on the guest system. The charm of backing up a virtual server on the host system is that disaster recovery is very fast. If your host system has hardware problems, you restore all virtual servers within minutes on another host with completely different hardware.
So I was quite curious to learn more about the VSS support of Virtual Server. I used the Backup Exec Advanced Open File Option which also supports VSS. I backed up a running virtual Windows Server 2003 system without any error messages.
I then deleted the virtual server and restored it using Backup Exec. The restored Windows Server booted without any problems. However, when I logged on, I got a message informing me that the system was shut down unexpectedly. The Windows Server worked perfectly, though.
But it is obvious that this is not the way it is supposed to work. The main problem with this method is that you can save the virtual machine files (.vmc .vhd . .vsv) of a running virtual server, but you can’t save the system memory this way. So you might end up with a backup where the virtual machine files are not in a consistent state.
It is not enough if the backup software just supports VSS. It also has to support the new Virtual Server VSS Writer service (VS Writer). This VS Writer can be used by VSS requestors to back up and restore virtual machines. That way, backup software can inform Virtual Server that is going to backup a virtual machine and Virtual Server can create a snapshot before the copy process starts.
This is how the documentation of Virtual Server 2005 R2 SP1 describes the procedure:
In the console tree of the backup program, browse to Microsoft Virtual Server.
Expand Virtual Server.
Select the virtual machines that you want to archive.
Select the Virtual Server configuration for archive.
Select the backup type.
Select the media to which you want to back up the data.
Start the backup.
So you don’t select the virtual machine files, but the virtual machine as a whole.
Symantec doesn’t yet offer such an agent for Backup Exec supporting Virtual Server. I googled a little to see if there is any other backup software vendor offering an Virtual Server add-on already, but I didn’t find any. I guess it won’t take too long until the major vendors will have such products as soon as the final of Virtual Server 2005 R2 SP1 is available. Considering the description in the Virtual Server manual, it seems as if there is at least one working together with Microsoft since NTBackup won’t support it.
I am curious if VMware will offer something comparable in the new future. I still prefer VMware Server for many reasons. However, the possibility of being able to backup running virtual servers is a killer feature. Because of its high price, VMware ESX Server is not yet an option for us.