[dm-devel] CLARiiON failover modes and DM.

[Tore Anderson]

* Paul Cote

> Is there a specific failover mode that the CX must be set for DM
> interoperability?

You have (at least) two options.  CLARiiON Open mode 1 is the 
traditional way where all paths to the passive controller is present but 
will refuse almost all I/O operations.  You'll need to be using the 
"emc" hardware handler for that to work, since a proprietary command 
needs to be sent to a path to the passive controller in order to 
trespass the volume there.

The other option (which is only available in FLARE 26) is ALUA mode 
(CLARiiON Open mode 4), where I/O is accepted on both controllers even 
though only one is the one handling all the I/O.  You can use this 
without a hardware handler (there's one in developement, though), but 
you'll still want to be prioritising the paths to the preferred 
controller for optimal performance.  This is the mode I would prefer, at 
least.  I wrote a bit more about the ALUA mode a few days ago:

http://thread.gmane.org/gmane.linux.kernel.device-mapper.devel/4366/focus=4435

Regards
-- 
Tore Anderson