Red Hat LINUX VIRTUAL SERVER 4.7 - ADMINISTRATION Installation Guide download pdf (Page 11)

Chapter 1. Device Mapper Multipathing

Device Mapper Multipathing (DM-Multipath) allows you to configure multiple I/O paths between server

nodes and storage arrays into a single device. T hese I/O paths are physical SAN connections that can

include separate cables, switches, and controllers. Multipathing aggregates the I/O paths, creating a new

device that consists of the aggregated paths.

1.1. Overview of DM-Multipath

DM-Multipath can be used to provide:

Redundancy

DM-Multipath can provide failover in an active/passive configuration. In an active/passive

configuration, only half the paths are used at any time for I/O. If any element of an I/O path (the cable,

switch, or controller) fails, DM-Multipath switches to an alternate path.

Improved Performance

DM-Multipath can be configured in active/active mode, where I/O is spread over the paths in a round-

robin fashion. In some configurations, DM-Multipath can detect loading on the I/O paths and

dynamically re-balance the load.

Figure 1.1, “Active/Passive Multipath Configuration with One RAID Device” shows an active/passive

configuration with two I/O paths from the server to a RAID device. T here are 2 HBAs on the server, 2

SAN switches, and 2 RAID controllers.

Figure 1.1. Act ive/Passive Multipath Configurat ion with One RAID Device

In this configuration, there is one I/O path that goes through hba1, SAN1, and controller 1 and a second

I/O path that goes through hba2, SAN2, and controller2. T here are many points of possible failure in this

configuration:

HBA failure

FC cable failure

SAN switch failure

Red Hat Enterprise Linux 4 DM Multipath

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Red Hat LINUX VIRTUAL SERVER 4.7 - ADMINISTRATION Installation Guide Page 11