Multipath I/O

In computer storage, multipath I/O is a fault-tolerance and performance enhancement 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
• Traffic shaping
• Automatic path management
• Dynamic reconfiguration

Multipath I/O software implementations

• Symantec Veritas Dynamic Multipathing (VxDMP) - a component of Veritas Storage Foundation or of Veritas Volume Manager, also sold as a separate product since Sept, 2010. The main advantages of DMP is it is cross platform, It is provided for Linux, Solaris, HP-UX, AIX and Windows. And it can also be run with any other volume manager also.
• AIX - MPIO Driver, AIX 5L 5.2 (October 2002) and later
• HP-UX 11.31 (2007)
• Linux - Device-Mapper Multipath . Linux kernel 2.6.13 (August 2005)
• OpenVMS V7.2 (1999) and later
• SGI IRIX - using the LV, XLV and later XVM volume managers (1990s and onwards)
• Solaris Multiplexed I/O (MPxIO), Solaris 8 (February 2000) and later
• Windows Server 2008 (February 2008) and later (Although Microsoft offered a multipath IO driver since (September 2002) for Windows 2000 server and later ; but it was not integrated in OS until windows server 2008)
• FreeBSD - GEOM_MULTIPATH and GEOM_FOX modules
• OpenBSD - mpath(4)
• NetBSD - using devicemapper from Linux (dm(4))
• Mac OS X Leopard and Mac OS X Leopard Server 10.5.2
• Novell NetWare 6.5 (July 2003)

Multipath software products:

• AntemetA Multipathing Software solution for AIX for HP EVA Disk Arrays
• Cambex Dynamic Path Failover for AIX
• NEC PathManager
• Promise Tech Perfectpath
• 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 StorageWorks 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
• Accusys PathGuard
• Infortrend EonPath
• Sun Multipath failover driver for Windows and AIX
• Sun StorEdge Traffic Manager Software, included in Sun Java StorEdge Software suite
• Apple Mac OS X
  • ATTO Technology multipath and failover driver supports Enterprise class Multipathing and Load Balancing for Celerity Fibre Channel Host Adapters in OS X for use with EMC, Hitachi, Xyratex and ATTO FastStream Storage Controllers
• Linux
  • multipath-tools, used to drive the Device Mapper multipathing driver, first released on September 2003
  • Fibreutils package for QLogic HBAs
  • RDAC package for LSI disk controllers
  • lpfcdriver package for Emulex HBAs
• Pillar Data Systems
  • Axiom Path Manager for AIX, Windows, Linux, and Solaris
• Areca Multipath failover driver for Windows
• iQstor MPA
• EIM OsnMpio V5.0 for Windows

See also

• Multipath (disambiguation)

External links

• VxDMP white paper, Veritas Dynamic Multi pathing.
• Solaris SAN Configuration and Multipathing Guide
• Linux Multipathing, Linux Symposium 2005 p. 147
• Linux Multipath Usage guide