DM-Multipath can be used to provide:

  • Redundancy 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.

  • Improved Performance Performance 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.

As part of redundancy/rebalance feature, the priority checker performs a very important role. But difference Vendor use different method to do it, here is a quick matrix.

See Table Priority Checker Conversion for a complete listing

Priority Checker Conversion

v0.4.8 v0.4.9
prio_callout mpath_prio_emc /dev/%n prio emc
prio_callout mpath_prio_alua /dev/%n prio alua
prio_callout mpath_prio_netapp /dev/%n prio netapp
prio_callout mpath_prio_rdac /dev/%n prio rdac
prio_callout mpath_prio_hp_sw /dev/%n prio hp_sw
prio_callout mpath_prio_hds_modular %b prio hds

Since the multipath config file parser essentially parses all key/value pairs it finds and then makes use of them, it is safe for both prio_callout and prio to coexist and is recommended that the prio attribute be inserted before beginning migration. After which you can safely delete the legacy prio_calliout attribute without interrupting service.

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