Did you (or someone else) removed or resized any SAN luns from non-working host recently ?
Or did you present a disk with same WWID as in some point in the past (same storage and host lun number, but different size) ?
Did you diff the output from multipath -ll from both hosts ?
If everything is okay (FC/host wise), you can always try rebooting the host that doesn't see the disks, rather then spending hours on fixing stuff like kernel sees lun sized xy and on storage is setuped and presented with different size and similar situations.
Couple of suggestions for future notice :
1. Have names in multipath.conf, it is more user friendly then 'mpathxy' generic name.
If you are creating documentation (you should
), it will be easier to write and maintain it.
2. Create one primary partition when giving disks to services, in this case ASM, don't give whole disks (first sector is for OS usage).