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We are using a Linux server running iscsitarget that we'd like to connect to a Windows 2008 server using multipathing.

Anyone have a link to good documentation on the steps necessary to configure the Windows side? So far, we've been unable to get the traffic to utilize more than 1 network connection.

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4 Answers 4

When you say you can't "get the traffic to utilize more than 1 network connection", there's two parts to it:

First, how many luns are you using Load balancing a single lun (one drive letter, so to speak) is much, much harder than load balancing multiple luns. You can get a huge head start by breaking the iSCSI share into two separate luns, then configuring iSCSI on the Windows box so that:

  • Windows network card #1 is the primary path for lun #1, and it points to Linux network card A
  • Windows network card #2 is the primary path for lun #2, and it points to Linux network card B (with a separate IP address)

This lets you bypass the one-connection limit in a duct-tape way, but you won't be able to get more than 1 network connection of throughput to a single lun at a given time.

Next, are you measuring send speeds or receive speeds?

To be able to send more than one network connection of traffic to an iSCSI device on the other end, you need to use MPIO on the Windows box and that's pretty much it. Configure MPIO with both IP addresses of the Linux host and you should be able to saturate two or more network cards of outgoing traffic.

However, to be able to receive more than one network connection of traffic on the Windows box, you're going to be pretty much out of luck unless you do something like channel bonding with your network cards. The Linux machine will only send traffic to one MAC address for one lun at a time. You can get around this by doing channel bonding so that the switch routes traffic for one MAC address through multiple network cards.

Here's a couple of my blog posts talking about the myth of active-active multipathing:

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Is the iSCSI initiator connected to your iSCSI target? If so, please check the following (from a Qlogic KB article):

For each Target Device, confirm that it can do Multi-Path Support. On the "Targets" tab, select the Target and click on the "Details" button. On the "Target Properties" dialog, with the "Session" tab selected, listed under the "This Target has the following sessions:", the Identifier will display two sessions for this Target. Select the "Device" tab and confirm that "MPIO Capable" setting for each Target Device is "Multi-Path Support".

For each individual Target, you can modify the "Load Balance Policy" setting. From the "Target Properties" dialog, individually select each Target Device listed and click on the "Advanced" button. On the "Device Details" dialog, select the "MPIO" tab. Select "Load Balance Policy".

ooops; this is for Initiator 2.0 (Windows 2003). I'm not sure if the 2008 initiator behaves the same way, I can test this out later today if you need to.

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There's a Microsoft whitepaper available on it: Windows Server High Availability with Microsoft MPIO

Otherwise the Microsoft Storage Area Networking blog might have some useful information.

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That white paper has about the same qualities as most of Microsoft's white papers -- it's a nice document to answer a checklist sales question, but nearly useless for doing an implementation. There's absolutely NO coverage of how to setup source / target adapters, etc. –  Steve Jun 12 '09 at 0:44

This is what you want - the Microsoft iSCSI Users Guide - it tells you how to configure the MPIO DSM as well as setting up and working with the MS iSCSI Software Initiator.

Whether the end result will actually make efficient use of the multiple adapters depends entirely on the compatibility of the default MPIO DSM with your target - most hardware iSCSI vendors build their own to ensure that the MS MPIO stack correctly optimizes load balancing for their array functionality.

When you say that you can't get it to use more than one network connection do you mean that you are not getting traffic load balancing or that you are not even getting path failover? If you follow the MPIO setup in the above you should get path failover at a minimum.

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