[dm-devel] CLARiiON failover modes and DM.

[Paul Cote]

Tore

I have found the definitions of all CX failover modes. The SAN admin
assigned failover mode 3. Will DM support option 3 assuming that I
follow EMC's guidance wrt the appropriate settings for the CX in
multipath.conf? ... Or should we reassign the failover mode to 1 per
your email? It seems to me that the path state status will differ
significantly based on the failover modes; specifically 1 or 3. We don't
have FLARE 26 so ALUA mode is N/A.

The failover definitions are:
1) Passive not ready; a command failure when I/O issued to non-owning
SP.
2) quiet trespass on I/O to non-owning SP
3) passive always ready; some commands (TUR) return "passive always
ready" status.

-----Original Message-----
From: dm-devel-bounces at redhat.com [mailto:dm-devel-bounces at redhat.com]
On Behalf Of Tore Anderson
Sent: Monday, November 19, 2007 1:51 PM
To: device-mapper development
Subject: Re: [dm-devel] CLARiiON failover modes and DM.


* 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/focu
s=4435

Regards
-- 
Tore Anderson

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