On 10/11/2016 08:22 AM, Hannes Reinecke wrote:

> Autodetection will only work if the hardware handler is loaded.
> If the handler is _not_ loaded autodetection won't work, either.
> And if we add this patch multipath will never load the modules, neither.
> So we need this functionality as a fallback if autodetect does not work.

I'm pretty sure all works flawlessly with this patch. Because I use similar
options for EMC VNX7500(CLARiiON) configured as ALUA "Failover Mode 4 
(Asymmetric Active/Active)",
with SLES-11/12 and RHEL-6 booting from SAN.

For SLES it was added to DGC config:
retain_attached_hw_handler yes
detect_prio yes

In RHEL it's included by default:
http://pkgs.fedoraproject.org/cgit/rpms/device-mapper-multipath.git/plain/0117-RHBZ-1198424-autodetect-clariion-alua.patch

And the modules are preloaded by multipathd/multipathd.service:
ExecStartPre=/sbin/modprobe -a scsi_dh_alua scsi_dh_emc scsi_dh_rdac 
dm-multipath


RDAC devices also depend *exclusively* on "retain_attached_hw_handler" and 
"detect_prio"
to run in ALUA mode.

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