Device Mapper Multipath is a storage target built on top of the core Device Mapper framework of the Linux kernel.
Following are some howto links for Device Mapper Multipath
RHEL / Cent OS HOWTO http://www.centos.org/docs/5/html/5.2/DM_Multipath/
DM-MP HOWTO from Sourceware http://www.sourceware.org/lvm2/wiki/MultipathUsageGuide
Below is an embedded page from the upstream DM-Multipath site. DM-Multipath Refspec
Device Mapper Multipath Workflows
The overall channel of communication for multiapth with helper tools.
Multipath Daemon Design