Red Hat Knowledgebase

The MSA series and StorageWorks Storage Array System (SAS) are mostly active/passive SANs, which means that one path is always active, and the other path does not do anything until the active side fails. It is not possible to safely use device mapper multipathing on these Storage Array Systems as it requires a special driver not provided with Red Hat Enterprise Linux 4. Some of these devices have upgradable firmware that can change the SAS to an active/active configuration which will allow device mapper to use multipathing. Please contact your hardware vendor to see if your device supports this configuration.