1.2. Overview of DM-Multipath
DM-Multipath can be used to provide:
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.
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
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. There are many points of possible failure in this configuration:
With DM-Multipath configured, a failure at any of these points will cause DM-Multipath to switch to the alternate I/O path.
Figure 1.2. Active/Passive Multipath Configuration with Two RAID Devices
hba1 to controller1
hba1 to controller2
hba2 to controller1
hba2 to controller2
In this configuration, I/O can be spread among those four paths.
Figure 1.3. Active/Active Multipath Configuration with One RAID Device