Multipath I/O

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In computer storage, multipath I/O is a fault tolerance technique whereby there is more than one physical path between the CPU in a computer system and its mass storage devices through the buses, controllers, switches, and bridge devices connecting them.

A simple example would be a SCSI disk connected to two SCSI controllers on the same computer or a disk connected to two Fibre Channel ports. Should one controller, port or switch fail, the operating system can route I/O through the remaining controller transparently to the application, with no changes visible to the applications, other than perhaps incremental latency.

Multipath software layers can leverage the redundant paths to provide performance enhancing features, such as dynamic load balancing or traffic shaping.

[edit] Multipath I/O implementations

Some operating systems support multipath I/O natively:

AIX - MPIO Driver, AIX 5L 5.2 (October 2002) and later
HP-UX - LVM pvlinks, HP-UX 10.0 (1995) and later
Linux - multipath driver. Linux kernel 2.4.17
Solaris Multiplexed I/O (MPxIO), Solaris 8 (February 2000) and later
Windows MPIO Driver, Windows Server 2003 (April 2003)
FreeBSD - GEOM_FOX module

Multipath software products:

AntemetA Multipathing Software solution for AIX for HP EVA Disk Arrays
EMC PowerPath
FalconStor IPStor DynaPath
Fujitsu Siemens MultiPath for Linux and Windows OS
Fujitsu ETERNUS Multipath Driver (ETERNUSmpd) for Solaris, Windows, Linux and AIX.
Hitachi HiCommand Dynamic Link Manager (HDLM)
HP Secure Path
NCR UNIX MP-RAS EMPATH for EMC Disk Arrays
NCR UNIX MP-RAS RDAC for Engenio Disk Arrays
ONStor SDM multipath
IBM System Storage Multipath Subsystem Device Driver (SDD), formerly Data Path Optimizer
Sun Multipath failover driver for Windows and AIX
Sun StorEdge Traffic Manager Software, included in Sun Java StorEdge Software suite
Linux
- multipath-tools, first released on September 2003
- Fibreutils package for QLogic HBAs
- lpfcdriver package for Emulex HBAs
Veritas
- Veritas Storage Foundation (VxSF)
- Veritas Volume Manager (VxVM)
Pillar Data Systems
- Axiom Path Manager for AIX, Windows, Linux, and Solaris