It's just to add a comment (tell me if it worth reopening the bug).
I've discovered that the more LUN mapped to a machine you have, the
more time the machine takes to boot (due to the IO errors) and well in
some situations it's not acceptable.
I've found on a centos ML that loading the scsi_dh_rdac kernel
module really early (in the initrd) could mitigate this issue. I've
made some test and it seems to work if the module is loaded in init-top
(and before udev). I'm not too sure this is possible to do, as it seems
that the 1st script to load (scsi) modules is the udev one.
The only suspicious message I get during boot is
"ldm_validate_partition_table(): Disk read failed." (two times). I
guess this is normal as I was doing my test with 1 LUN (2 active paths
and 2 inactives), the boot seems faster and no IO error can be seen.