Yes, some sort of multipathing software is obviously required.
The device-mapper-multipath system available in modern Linux distributions (and recommended by RedHat) is a manufacturer-agnostic solution. It can identify the disks using standard WWID numbers or a collection of known manufacturer-specific identification methods. It presents a third set of devices, where each device refers to a particular disk using any and all available paths.
There are two ways of naming the multipathed disk devices in device-mapper-multipath. If the FriendlyNames option is enabled in /etc/multipath.conf, the default names are like /dev/mapper/mpath
, where is a number. If FriendlyNames is off, the default name is /dev/mapper/ where is a long string of hexadecimal digits guaranteed to be unique for each disk/LUN by the storage manufacturer.
Device-mapper-multipath does not hide the /dev/sd* devices corresponding to individual paths, so that with 8 LUNs with 2 paths each you would see 16 /dev/sd* devices and 8 multipath devices. This allows you to use the /dev/sd* devices if you have a specific need to avoid multipathing, e.g. if you wish to measure the performance of a particular path. You can use the "multipath -l" command to see how the multipath devices are mapped to /dev/sd* devices and the states of each individual path.
Some FibreChannel HBA manufacturers offer versions of HBA drivers for Linux that include multipath functionality. These drivers require at least two HBAs from the same manufacturer and their load-balancing features may be limited to failover-only.
Device-mapper-multipath can do load balancing between multiple paths if the storage system allows simultaneous use of both paths (i.e. active/active multipathing). On the other hand, multipath solutions built into HBA drivers may hide the presence of multiple paths and allow the system to be administered just like with regular single-pathed disks.
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