Multi-path I/O provides storage with improved fault-tolerance and performance by providing more than one physical path between the server and storage elements. A simple example would be a server with multiple HBA’s attached via a SAN to two arrays. If the path or storage element from one HBA fails, multi-path I/O software would allow seamless connection via the other path to the storage devices. The only impact would be a possible change in latency.
The most important benefits of multi-path I/O software are:-
- Improved availability,
- Dynamic load balancing,
- Storage network traffic shaping,
- Dynamic reconfiguration.
Previously, most software came from storage vendors as support for their own storage arrays. Example of this software include EMC’s PowerPath, FalconStor IPStor DynaPath, Hitachi’s HiCommand Dynamic Link Manager (HDLM), HP’s StorageWorks Secure Path and IBM’s System Storage Multipath Subsystem Device Driver (SDD). Most of these packages are provided with chargeable software licenses.
Recently, native multi-pathing technologies in operating systems like Windows, Linux, and HP-UX have advanced in function and stability. Most of these software packages come free of charge, which has increased the momentum for adoption. Examples include the Windows MPIO driver, AIX - MPIO Driver, HP-UX 11.31 and beyond, Solaris Multiplexed I/O (MPxIO), and Veritas Dynamic Multi-Pathing (DMP, part of the Veritas Storage Foundation).
The availability of this multi-path support in the server operating systems allows IT installations to adopt a more sensible server-led strategy that is independent of the storage array vendors. This strategy makes testing and migration much easier and is the logical strategy going forward. It will allow more effective implementation of federated storage solutions, and the implementation of true non-disruptive migration strategies.
IBM’s XIV array is a good example of this trend. IBM has not announced any separate multi-path I/O package for the XIV but relies solely of native multi-path I/O support from operating systems and Veritas. IBM recently announced good GUI and graphical XIV support for OS-led multi-path support.
Action Item: CIOs, senior IT management and storage managers should move from storage array-led multi-path I/O strategy to an operating system-led strategy. They should ensure that any array purchased has support for all the operating systems that are present in the data-center. If a proprietary package is bought or retained, it should be widely supported by storage array manufacturers. Storage vendors should move to supporting multi-path I/O natively in all the operating and file systems supported. Legacy storage vendor specific multi-path I/O packages should be phased out.
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