Microsoft’s in-box disk multipathing is a good thing…
Posted on 16 December 2008
I’ve been spending some of my time implementing the storage vendor supplied widget that fits into Microsoft’s MPIO solution. MPIO is short for Multi-path I/O. What is that? It is the ability to have more than one physical connection to your storage device. Why would you want that? For redundancy and performance. The concept and storage vendor specific implementations have been around for a long time. Microsoft first introduced MPIO as an add-on available only from storage vendors as part of Windows Server 2003. Microsoft then decided to add it to the OS distribution in Windows Server 2008. So if you are running 2008, you have it. The storage vendor supplies a widget called the Device Specific Module (DSM). The DSM is responsible for selecting which path an i/o request (think read or write) will take to the storage device. Now this can be a bit complex in large Storage Area Networks (SANs) and it can be very simple in directly attached SAS drives. Remember SAS drives have two ports, not one like the old parallel SCSI drives. So every SAS drive is capable of taking advantage of MPIO. Check out Microsoft’s FAQ.
If you’re trying the new Windows Server 2008 R2 check out this. for the latest information. There are also command line tools for when you’re using Server Core.
So if you have specific questions regarding MPIO and would like a second opinion or an independent (I’m not a Microsoft employee) opinion feel free to toss questions at this post or at my email address (see Sales tab).
It feels like I know just about all there is to know about the moving parts in this solution and how to effectively manage it in large environments.
Check out my blogroll, there are a few Microsoft blogs worth catching if you’re working on understanding what this is and how to take advantage of it. It offers some goodness in-box that usually costs a lot of extra money from the storage vendors. So be careful to ask your array vendor if they support Microsoft’s MPIO and if support costs extra. It just might save you a few thousand dollars per host which is nothing to take lightly these days.
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