[CentOS] Help setting up multipathing on CentOS 4.7 to an Equallogic iSCSI target

Sat Mar 14 16:28:30 UTC 2009
Ross Walker <rswwalker at gmail.com>

On Mar 14, 2009, at 5:50 AM, James Pearson <james-p at moving- 
picture.com> wrote:

> 2009/3/13 Ross Walker <rswwalker at gmail.com>:
>> With open-iscsi you will need to use multiple iSCSI sessions over
>> different subnets and dm-multipath. Configure 2 portal addresses one
>> in each subnet. If Equalogics sets the SCSI Ids correctly then dm-
>> multipath will match them up. Set a round-robin policy on the paths
>> and test/tune accordingly (path delays, # blocks per path, etc).
> I have tried using separate subnets on the different interfaces on the
> Equallogic box and host - but the client host would still only find
> the volume once.
> I've now heard back from Dell - and it appears it can't be done with
> the software initiator on CentOS4/RHEL4 - but should work with CentOS5

Did they give a reason why?

You could ask on the open-iscsi list too.

I thought if it treated each ip as a separate target portal on the  
initiator you would be able to connect to two "different" targets at  
the same time and let dm-multipath figure out it's the same disk. No?

I think what is happening is open-iscsi (on 4) only recognizes the  
first target sent during a SendTargets request, but the first target  
in the list should always be the one on the current ip address of the  
portal, so if you list each ip address for discovery in theory it  
should discover the target for each ip. Now if Equalogics gives the  
same target list irrespective of the portal ip it's called on then I  
can see where the problem is.

A tcpdump during login/discovery should show this easy. Just look at  
the sendtargets list for each portal in wireshark and if they are in  
the same order then there's your problem.