Duplicati hyper-v


I want to backup my windows server with duplicati.
The server is running different hyper-v machines and I want to backup one of them.
I don’t know what would be better: to backup the hyper-v snapshot itself or inside the hyper-v machine the files that need to be backupped.

When backing up the hyper-v machine, will duplicati only copy the used disk size or also the available space ?

The hyper-v machine containes an Exchange Server and an SQL Server. When backing up the hyper-v machine, will it also truncate the logs of Exchange and SQL?

Or if I backup inside the hyper-v machine: is there a way to truncate the logs after backing up the files of Exchange and SQL?

Kind Regards,


I have only limited experience with Duplicati and Hyper-V, so I could be wrong… but I thought I’d take a stab at your questions.

Duplicati’s Hyper-V “integration” is pretty rudimentary, I think. It allows Duplicati to automatically determine which files on the host are related to the VM you selected for backup. When you perform the actual backup, it backs up the raw files (vhd/vhdx, etc) as if you selected them directly through the normal file browse dialog.

So I don’t think Duplicati has any knowledge of which “sectors” of a VHD are in use vs which are not. It reads the file on the disk just like it reads any other file.

I did a test where I created a VM and set the disk to fixed size of 1GB. I did not install an OS in the VM. I ran a backup and Duplicati processed the whole 1GB, but of course it compressed really well since it was all zeros. So in a sense parts of the disk that have never been used will not consume much space on the backup. But parts of the disk that have been used at one point but have since been deleted probably will, because the data is still technically there in the disk.

I’m fairly certain the answer is NO. I have experience with enterprise-grade backup systems, and in order to do SQL or Exchange log truncation you need to have some sort of agent installed inside the VM to trigger that type of action. Backing up the VM from the outside (host point of view) wouldn’t do it.

Duplicati has some integration ability with MS SQL, but I have never personally tested it. I’m going to guess that the integration is rudimentary, similar to Hyper-V: it just lets Duplicati figure out which physical files are related to a particular SQL database you selected for backup, and then it backs them up raw. It probably does not do any sort of log truncation. Again I could be totally wrong, I don’t use SQL myself at home so I’ve never tested Duplicati with it.

It has no integration with Exchange at all.

In my opinion Duplicati is a great backup option for home users but I would not use it for enterprise systems like MS SQL, Exchange, etc.

If you really want to use Duplicati to back up MS SQL, I’d probably set up a maintenance plan for SQL that dumps the databases to BAK files, truncate logs, etc. Then use Duplicati to back up the BAK files.