[dm-devel] Using different configuration for arrays with identicalvendor/product

[Tore Anderson]

* berthiaume_wayne at emc.com

> 	You should be able to use the emc_handler for both arrays.
> Depending on the distro you are using only implicit ALUA is supported,
> explicit ALUA is in being worked on for upcoming distros. Whether the
> storage group within the array attached to the server is ALUA or not is
> determined by the failover mode you set for the host on that array. At
> the server side you will not know the difference between the two
> failover modes, PNR or ALUA.

Hi Wayne, thanks for your reply.

So I can use the emc_clariion hardware handler towards an array
configured for ALUA mode.  Wasn't aware of that.  I feel it's better to
let the array handle the trespassing on its own based on the ratio of
«non-optimal» I/O operations (using hardware_handler 0), but I can live
with host-initiated trespasses on PG swithces/inits.

Anyway - there's still the problem of the path_checker.  If I'm using
«emc_clariion» for the array configured for ALUA mode (CLARiiON Open,
mode 4), all paths is perceived to be failed.  If I'm using «tur» for
the array configured for PNR mode (CLARiiON Open, mode 1), the passive
path is perceived to be failed.

Hence, if I use «emc_clariion» I won't be able to access the volumes on
the CX3-40 at all, while if I use «tur» dm-multipath won't switch PGs
when there's a (real) failure on the active path to the CX200.  None of
these are acceptable alternatives for production use, so the only
workaround I've found so far is to configure the CX3-40 to use PNR mode
(which sucks since ALUA is way better).  Do you have another trick up
your sleeve for me?

Regards
-- 
Tore Anderson