I am trying to mount Linux VM's hdd but not able to do it
Parallels Mounter does not support .hdd with LVM on Mac OS X
To apply a workaround, please follow these steps:
Create new VM with Linux (with just LiveCD.iso mounted) on the same MacMini server, and configure this VM to use .hdd file from Ubuntu VM that you want to restore.
Boot this new VM into LiveCD.iso and mount LVM partition.
After you get access to the data you may copy it via network or on USB disk.