Red Hat ENTERPRISE LINUX 5 DM MULTIPATH Configuration And Administration Manual page 12

Chapter 1. Device Mapper Multipathing
• HBA failure
• FC cable failure
• SAN switch failure
• Array controller port failure
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"
shows a more complex
active/passive configuration with 2 HBAs on the server, 2 SAN switches, and 2 RAID devices with 2
RAID controllers each.
Figure 1.2. Active/Passive Multipath Configuration with Two RAID Devices
Figure 1.2, "Active/Passive Multipath Configuration with Two RAID Devices",
In the example shown in
Figure 1.1,
there are two I/O paths to each RAID device (just as there are in the example shown in
"Active/Passive Multipath Configuration with One 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
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