I own a QNAP TS-549 Pro+ that I am quite happy with. I customized it quite a lot using ipkg but with the Optware ts509 repository being abandoned for almost a year now, I really need to update my software. As a long time Debian user OMV seems like a natural fit.
Upon researching I read:
ZitatOpenMediaVault does not support a data partition on the device where the operation system is installed. Therefore, please note that the whole disk device is occupied by the operation system. During the setup the device is parted into a partition used by /root and a swap partition. All existing data on drive are deleted during installation!
Indeed, testing in a VM shows that the entire disk is wiped and reformatted without warning. Good thing this is in bold on the wiki. 
On my QNAP I have about 6 TB of data in an md RAID 5 that I would really like to keep. I feel confident in installing Debian Wheezy on my QNAP with / on a md RAID 1 (and /boot on the QNAP flash) and then adding OMV to it. So in the end the data and system partitions will share the physical disks. According to this answer OMV does support this.
Is anyone else running OMV on QNAP hardware? Is there something I am missing?