This article describes how to mount a Linux Logical Volume Manager (LVM) partition located inside a virtual disk (VDI) in a XenServer Host.
I have never been a fan of logical volume management which seems to be a Red Hat thing. It completely complicates matters when mounting drives. XenServer, which is based off centos (I think) is littered with LVMs as the result of performing the above procedure will attest. I hope Citrix had a good reason for doing this.