You need some mechanism to ensure mutual exclusion amongst the two machines,
or else they will trash each other's data.
There's a piece of software called GFS (http://www.sistina.com/gfs). I
haven't tried it out, but it promises:
The Global File System (GFS) is a shared disk cluster file system for Linux.
GFS supports journaling and recovery from client failures. GFS cluster nodes
physically share the same storage by means of Fibre Channel or shared SCSI
devices. The file system appears to be local on each node and GFS
synchronizes file access across the cluster. GFS is fully symmetric, that
is, all nodes are equal and there is no server which may be a bottleneck or
single point of failure. GFS uses read and write caching while maintaining
full UNIX file system semantics.
I'm not sure if GFS can work on top of XFS, or if it's a replacement for it.
I also don't know if it'll run on IRIX. There are probably other commercial
applications that'll do what you want, but they'd be pretty expensive..
>I envision to make a filesystem, such that when a file is created
>on either one system, it is visible directly on the other opposite
>system.... Your FAQ indicate that it is possible to bring over XFS disks
>from IRIX environment to the Linux environment, so,