Oracle RAC with ENBD

Hi !
Is it possible/recommended to use ENBD for shared storage?
Actually, our DBA`s evaluate Oracle RAC on shared storage based on scsi and firewire - but i`m 
thinking about a scenario with two virtual linux systems (on vmware) using a networked block device.
There is a paper from someone, who did this with NBD: http://www.fi.muni.cz/~kripac/orac-nbd/


but - reading this: http://www.polarisdb.com/rac.htm

>I looked into several open source software solutions like NBD, ENBD, DRBD, and PVFS. 
>Unfortunately, each solution either wasn't designed to support multiple node concurrent 
>access or didn't allow support for parallel concurrent writes. Interestingly, the author 
>of DRBD indicates that adding this support wouldn't require much effort.

drives me crazy a little bit.
So - multiple node concurrent access doesn`t even work with NBD ? 
How can that work, what the author from the first link did?

Is a NBD suitable for shared storage and can NBD/ENBD used for this?
Could please someone give a comment about this?


wish you merry christmas!

roland