Windows MPIO with IBM storage

IBM mid-range storage systems (like DS3950) work in active/passive mode. It means that access to each LUN is given through one controller, in constrast to active/active storage where data between host and two controllers can flow in round-robin fashion. So redundant path here is used only as a failover. Software which provides this failover functionality is called Multipath I/O (MPIO) and has implementations for all operating systems. I’ll desribe how to configure MPIO version for Windows.

Installation

Prior to Windows Server 2008, Microsoft didn’t have its own MPIO implementation and MPIO was distributed with IBM DS Storage Manager product. Now you can install MPIO from “Feautures” sub-menu of Windows Server 2008 Server Manager. After installation is complete you will find MPIO configuration options under Control Panel and in Administrative Tools.

IBM storage works well with default Windows MPIO implementation, however it’s recommended to install IBM MPIO (device-specific module) from Storage Manager installation bundle. In my case MPIO installation file was called SMIA-WSX64-01.03.0305.0608.

Enable multipathing

Initially you will see two hard drives for each LUN in Device Manager. You can enable MPIO for particular hardware ID (in other words, storage system) on Discover Multi-Paths tab of MPIO control panel. You can’t do that with LUN granularity. After you add selected devices and reboot, you will see them on “MPIO Devices” tab. Now each LUN will be seen as a single hard drive in Device Manager.

Configure preferred path

MPIO supports several load-balancing policies, which are configured on a LUN basis from MPIO tab of a hard drive in Device Manager. As a Load Balance Policy select Fail Over Only. Then for each path select which is Active/Optimized and which is a Standby path. Also make active path Preferred, so that after failover it failbacks to it.

Don’t be confused by iSCSI on the figure. It’s the same for pure FC. It’s just for reference.

Check configuration

When you configure active and passive paths you assume that first path listed is to controller A and second path is to controller B. But, in fact, there is no indication of that from the configuration page and you can neither confirm nor deny it. The only ID you see is adapter ports but they don’t even map to the actual ports on HBAs.

To be able to check your configuration you need to install IBM SMdevices utility which comes with IBM DS Storage Manager. Run DS SM installation and go for Custom Installation. There you need to check only the Utilities part. In SMdevices output you can see which path is preferred for this LUN and if it’s configured as active (In Use):

C:\Program Files\IBM_DS\util>SMdevices
IBM System Storage DS Storage Manager Devices
. . .
\\.\PHYSICALDRIVE1 [Storage Subsystem ITSO5300, Logical
Drive 1, LUN 0, Logical Drive ID
<600a0b80002904de000005a246d82e17>, Preferred Path
(Controller-A): In Use]

References

The best reference I found on that topic is IBM Midrange System Storage Hardware Guide (SG24-7676-01), from p.453: DS5000 logical drive representation in Windows Server 2008. As well as Installing and Configuring MPIO guide from Microsoft.

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One Response to “Windows MPIO with IBM storage”

  1. IBM DS Storage and Windows MPIO « Bart's Weblog Says:

    […] Windows MPIO with IBM storage https://niktips.wordpress.com/2012/09/17/windows-mpio-with-ibm-storage/ […]

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