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[dm-devel] Re: [PATCH] RFC: have dm-mpath use already attached scsi_dh



Hannes Reinecke wrote:
Hi Mike,

michaelc cs wisc edu wrote:
From: Mike Christie <michaelc cs wisc edu>

If you have a mixed environment of clarriions, where some
support ALAU and some support PNR, what do you put in
your multipath.conf? With this patch you do not have to worry about
it. If those modules are loaded before dm-mpath, then they
will have attached to the correct devices based on inquiry, alua commands
and parsing of data buffers (for example in scsi_dh_emc's alua check).
There is no need for the user to set that info in the multipath.conf.
And in general since all scsi_dh_modules will attach to the devices
they work for, we do not need to have users specific this.

No. The problem here is the hardware table from scsi_dh is compiled
in and cannot be changed from userland. The multipath.conf OTOH
is purely user-defined and, what's more, the user might have a valid
reason for modifying it.
(EG EMC Clariion can well be run in PNR mode even though ALUA is
active, or the user might want to try ALUA on any as-of-yet unknown
devices)

Ah. I misread the code and misunderstood the compat mode. I thought scsi_dh_emc was failing the attach when ALUA support was detected.


So _not_ allowing multipath to override the device handler setting
will just add to the confusion and makes error tracking even more
difficult.

So I would prefer the attached patch, it even save to touch
device handler code at all.


Thanks. I think this will work for me.

Are you going to push this for 2.6.30?


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