Hyper-V Backup issue

Hi,

We are using Dell Server and Installed Windows Server 2012 , Hyper-V role on it.

We have created multiple virutal server inside it for Database Server , Exchange Server , IIS etc.

Now , When we are trying to take a backup using Windows Server Backup Utility it gives error.

When we are trying to backup a full bare metal recovery backup it fails with error " there is no sufficient space available on remote and local server " , Although , we do have a enough space available on our Synology NAS Backup device as well as on local server.

When we try to take only system state or c drive backup it works..so what could be the issue.

Thanks,