Microsoft Multipath I/O: Frequently Asked Questions

Multipathing solutions use redundant physical path components–adapters, cables, and switches–to create logical "paths" between the server and the storage device. In the event that one or more of these components fails, causing the path to fail, multipathing logic uses an alternate path for I/O so that applications can still access their data.

Although both multipathing and clustering result in high availability and improved performance, they are not equivalent concepts. While clustering provides high application availability and can be implemented using a multipathing solution, multipathing provides high storage availability and does not require a clustering solution. Clustering is the use of multiple computers, interconnects, and storage devices that work together to provide users with high application availability from what looks like a single system. Multipathing, as stated in the previous question, is the redundancy of the storage network components (the cabling, adapters, and switches) to provide users with high storage availability.

All Microsoft-supported multipath solutions are listed in the Windows Catalog. To locate your solution, visit the Server Hardware Catalog and then, in the "Search for" field, enter "MS MPIO."

Contact your storage provider. Microsoft is working to add this information to future versions of the Windows Catalog.

Contact your storage provider to find out if your multipath solution is Microsoft MPIO-based.

You can find more information, including a white paper on Highly Available Storage, on the Microsoft Storage Web site.

The Microsoft MPIO Device Specific Module (DSM) is responsible for all aspects of cluster interoperability. Users must find out the level of support from the provider of the Microsoft MPIO solution.

Yes, Microsoft MPIO is fully compatible with the Microsoft iSCSI Initiator.

Yes, current Microsoft plans are to provide an MPIO-based multipathing solution that is based on relevant SCSI standards (SPC-3) in Windows Longhorn.

Yes, Microsoft MPIO is specifically designed to run on both platforms. Microsoft uses the same set of foundation MPIO drivers on both. This lets customers upgrade a server from Windows 2000 Server to Windows Server 2003 with a Microsoft MPIO solution in place, instead of having to remove it and disconnect the storage before upgrading.

Yes. Go to news://msnews.microsoft.com/microsoft.public.storage, the public newsgroup that you can use for Microsoft MPIO-related questions.

Yes, the Microsoft iSCSI Initiator v2.0 released in June 2005 includes an industry-standard Microsoft MPIO DSM. Additionally, Microsoft provides the source code for this DSM to its Microsoft MPIO partners as part of the Microsoft MPIO Driver Development Kit (DDK). Partners are free to use this source code as a base for developing their own MPIO DSM.

Microsoft MPIO was designed to be a high-performance platform, but performance depends on the actual implementation of the Device Specific Module (DSM), not Microsoft MPIO.

Yes. Microsoft MPIO enables coexistence for multiple vendors' solutions, which many customers consolidating servers and storage want.

Yes. The Microsoft industry-standard DSM for Fibre Channel is planned for inclusion in Microsoft Windows Server code-named Longhorn.

Customers want Microsoft MPIO-based solutions for both reliability and supportability reasons. Microsoft MPIO was designed specifically to work with the Microsoft Windows operating system, and Microsoft MPIO solutions are tested and qualified by Microsoft for compatibility and reliability with Windows. Many customers do require that Microsoft support their storage solutions, and Microsoft MPIO is no exception. With a Microsoft MPIO-based solution, customers will be supported by Microsoft should they experience a problem. For non-Microsoft MPIO solutions, Microsoft support is limited to a "best effort" type of support only, and customers will be asked to contact their MPIO solution provider for assistance.

Windows Server 2000, Windows Server 2003 and Windows Server 2003 R2

x86, x64 and IA-64

You can download the Third-Party Multipath and MPIO Test and Submission Process white paper for more information.

Microsoft designed the Microsoft MPIO program to provide a foundation for other storage vendors to create a multipath solution that is integrated into the Microsoft Windows architecture. Microsoft MPIO is a key Microsoft initiative to make Windows the best platform for storage. The Microsoft MPIO white paper provides more details on the Microsoft MPIO architecture. Vendors may also send questions to MPIOpm@microsoft.com.

Here are a few Microsoft partners that have created Microsoft MPIO: HP, IBM, Hitachi, Fujitsu, Toshiba Solutions, Veritas, Egenera, NEC, Unisys, XIOtech, and Maranti. More partners are offering Microsoft MPIO solutions all the time.

Microsoft MPIO solutions are based on redundant hardware paths from the Windows Server to the storage array. The Microsoft MPIO program requires that the multipath solution be "HBA agnostic" and focuses on path selection for failover and/or load balancing at the "midlevel" of the Windows architecture. The only requirement is that the HBA follow the standard mini–port driver model. Ask your HBA vendor for more information.

Yes, your company must sign the Microsoft MPIO Agreement and use the Microsoft MPIO Driver Development Kit (DDK) to develop a Device Specific Module (DSM) that works with your storage. If your storage complies with the SCSI Primary Commands revision 3 (SCP-3) standard, you can use the Microsoft-provided sample DSM as is for your solution.

The sample DSM code is part of the MPIO Driver Development Kit (DDK). You can request information about that Microsoft MPIO program by sending mail to MPIOpm@microsoft.com.

Shared LUNs in a clustered environment can be used only in failover mode. Load balancing in a cluster environment can be achieved by the MPIO Device Specific Module (DSM) using Persistent Reservation.

The iSCSI DSM implements Persistent Reservation and the source code is included in Microsoft MPIO Driver Development Kit (DDK).

Features of the SNIA multipath management API can be implemented in the MPIO DSM. The foundation support for the load balancing, failover, and failback policies defined by SNIA exists in Microsoft MPIO today. The sample DSM code is included in the Microsoft MPIO Driver Development Kit (DDK).

Yes. The multipath Microsoft "Designed for Windows" Logo Program (add–in program) for iSCSI is a new program and requires that all multipath solutions be based on Microsoft MPIO.

Yes. All of the device types listed in the driver information file must be attached to the test system and used by the multipath test cases. An exception is granted for multipath submissions with a driver information file that contains multiple storage devices within the same family. For this case, testing with one storage device from the family is sufficient. For more information on the submission process, read the Third–Party Multipath and MPIO Test and Submission Process white paper.

Microsoft has developed an "industry standard" DSM for iSCSI. Microsoft is also in the process of developing one for Fibre Channel. These solutions are intended to work only with storage compliant with SCSI Primary Commands revision 3 (SCP–3). Ask your storage provider for more details.

Yes, if the non–Microsoft vendor–specific solution "claims" only the storage devices that it supports.