Red Hat DEVICE-MAPPER MULTIPATH 4.6 Configuration And Administration Manual page 13

Overview of DM-Multipath
Figure 1.2. Active/Passive Multipath Configuration with Two RAID Devices
As in the example shown in Figure 1.1, "Active/Passive Multipath Configuration with One RAID
Device", there are two I/O paths to each RAID device. With DM-Multipath configured, a failure at
any of the points of the I/O path to either of the RAID devices will cause DM-Multipath to switch
to the alternate I/O path for that device.
Figure 1.3, "Active/Active Multipath Configuration with One RAID Device" shows an active/active
configuration with 2 HBAs on the server, 1 SAN switch, and 2 RAID controllers. There are four
I/O paths from the server to a storage device:
• hba1 to controller1
• hba1 to controller2
• hba2 to controller1
• hba2 to controller2
In this configuration, I/O can be spread among those four paths.
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