I want to be able to read data from the Hyper-V VMs on the host. I understand I can go to DISM and attach VHD there - but it requires a VM to be offline - otherwise I get the following error:
Virtual Disk Manager
The process cannot access the file because it is being used by another process.
Are there any ways to achieve this while keeping VM online? I want this primary for making backups easier.
If your goal is backups, then you should be using Hyper-V aware backup software (something that uses the Hyper-V VSS writer). While the VM is running, the .vhd/.vhdx file is locked.
If you want to backup files within the VM, then use any backup software you like that will backup flat files/sql/exchange/whatever.
It sounds like the VM portion it throwing you off. Take that out of the equation, treat it like a standard computer and find a backup solution that works for you.