Device Mapper Multipathing; Overview Of Dm-Multipath - Red Hat DEVICE-MAPPER MULTIPATH 5.2 Configuration And Administration Manual

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. These 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. 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"
active/passive configuration with two I/O paths from the server to a RAID device. There are 2
HBAs on the server, 2 SAN switches, and 2 RAID controllers.
shows an
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