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

George Negoita wrote:
> Hello,
>
> On Fri, Mar 13, 2009 at 5:36 PM, James Pearson
> <james-p@moving-picture.com> wrote:
>
>>I'm trying to test out an Equallogic PS5500 with a server running CentOS 4.7
>
>
> Try reading this:
> http://linfrastructure.blogspot.com/2008/02/multipath-and-equallogic-iscsi.html
> http://lists.centos.org/pipermail/centos/2008-June/059358.html
> http://www.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5.2/html/DM_Multipath/index.html
> http://kbase.redhat.com/faq/docs/DOC-2877
>
> This is what helped me understand how to setup dm-multipath on centos
> 5 using iet iscsi target.

I'm using CentOS4.7 - the iscsi initiator set up appears to be different
in CentOS5 ...

Thanks

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

On Mar 13, 2009, at 1:50 PM, James Pearson <james-p@moving-
picture.com> wrote:

> nate wrote:
>>
>> Dell should be able to tell you this.
>
> That's what I thought ... I asked if I could get more than 2Gbit+/sec
> throughput to a single target from a single host - they said yes, but
> have not (yet) provided any useful information on how to actually set
> this up. I have a support call open, but I thought I'd ask here as
> well
> - just in case anyone else had actually done this with this type of
> storage.

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).

With Windows initiator you can do multiple connections over different
subnets to the same iSCSI session which is more efficient, but I don't
know if Equalogics supports that. You will need MS multipath for this
to work too.

802.3ad balances hosts/connections between interfaces so each host or
connection is limited to 1Gbps which does no good for the initiators
but allows the target to handle more initiators if it supports it.

-Ross

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

2009/3/13 Ross Walker <rswwalker@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

Thanks

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

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

> 2009/3/13 Ross Walker <rswwalker@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.

-Ross

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