Running SLES 11sp3 with XEN virtualization.

The host partition table has a 3TB allocated to /dev/sdb
The vm's partition table has the 3TB /dev/xvdb2 which is mounted as /var/data

My VM is running SLES11sp3 as 100gb image containing the OS and other stuff. I want to run a backup of the VM's raw disk image and the /var/data.
So from the host, I shut down the VM and I can then backup /var/lib/xen/images/archive/disk0.raw. All good so far.

Now I need to access the /var/data on the VM.
So my thinking is mount 3TB VM partition on the host as "mount /dev/sdb /mnt/data"
Then run the backup and then umount /mnt/data and restart the VM.

So will this work, break stuff or cause chaos ..... or is there a better way?
Your thoughts will be appreciated.