[dm-devel] RE: How is the multipath pg policy group-by-nodename any differen t than the failover policy?

[Arthur Bergman]

On 28 Apr 2005, at 19:53, goggin, edward wrote:

> On Wed, 27 Apr 2005 21:38:34 +0100, Arthur Bergman wrote:
>
>> All the path have the same serial, but the show up from different 
>> nodes.
>
> Not sure what this means.  The group-by-node-name policy implies 
> assigning
> paths with similar node name attribute to the same group.  For SCSI, 
> seems
> like the multipath configurator assigns the node name attribute to be 
> the
> combination of SCSI initiator and target addresses (in linux, host
> no/channel no/target id).  This should be different for every path 
> which
> would cause each path to be assigned to a different path group.
>
> How is the resultant path grouping any different than if you used the
> failover
> path grouping policy instead?
>
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Huh, as far as I understand it group_by_nodename uses the

/sys/class/fc_transport/target0:0:0/node_name information

from our setup, there are 8 paths to two controllers, there is no 
failover cost but it defeats read caching pretty beadly to use both 
controllers..

/sys/class/fc_transport/target0:0:0/node_name:0x50050768010003d5
/sys/class/fc_transport/target0:0:1/node_name:0x5005076801000361
/sys/class/fc_transport/target0:0:2/node_name:0x50050768010003d5
/sys/class/fc_transport/target0:0:3/node_name:0x5005076801000361
/sys/class/fc_transport/target1:0:0/node_name:0x5005076801000361
/sys/class/fc_transport/target1:0:1/node_name:0x5005076801000361
/sys/class/fc_transport/target1:0:2/node_name:0x50050768010003d5
/sys/class/fc_transport/target1:0:3/node_name:0x50050768010003d5


So all path that ends at a matching node_name, even if they are on 
different transport targets get one path.

Cheers
Arthur

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