I am in an interesting situation and uncertain about the optimal or safe way to proceed.

I have a client that has a physical server that is set up with OVM. (Basically Xen, supported by Oracle.) I have set up two HBAs on the physical server, and can see all 140+ paths to all their SAN luns. Those paths show up as /dev/sd* devices.

Also, for now, I set up multipathing on the physical host. So we have all sorts of nice device files in /dev/mapper that map to the LUNs. I can easily undo that if need be.

Do I want to attempt to make the /dev/mapper/* files visible to the guest OSes? (If so, I'm wondering if there's a risk of the VMs attempting to start before the /dev/mapper/* files appear on the physical host.)

OR, is the correct methodolgy simply to make all /dev/sd* devices available to each guest OS, and set up multipathing individually on each guest OS? (It's okay with multiple hosts writing to the same LUN - Oracle manages all of that. There's no mounting of ext3 filesystems to multiple hosts going on here.)

I'm completely new to Xen. Any suggestions or warnings greatly appreciated!

Haven't done this at all but was curious.

Based on document I found on EMC PowerLink for PowerPath their procedure seems to be to create the the multipath device in the Xen base then allocate that multipath device to the Xen virtual hosts you create. There's more to it than that in their document but I think that answers your base question.

You didn't say what you're using for multipathing or what the array is.