Linux Multipath is a device-mapper target auto configurator and a daemon that enforces the path policy.
Getting started with Multipath is easy:
sudo apt-get install multipath-tools multipath-tools-boot
Many Multipath implementations exist for Linux from commercial vendors like EMC PowerPath. Linux Multipath is the default implementation that is supported by the community and is quite reliable. Many transports are supported: Fibre Channel, iSCSI, and SAS to name a few.
- Ubuntu Server Official Multipath Documentation
- multipath-tools Launchpad Home
- Definition Overview: http://en.wikipedia.org/wiki/Multipath_I/O
- Multipath Design, Linux Symposium Vol 1, p147-168
- Multipath Homepage
- Device Mapper Resource Page
- Multipath Wiki
It's important to understand what you're working with when configuring a SAN.
Also most SANs include a sample multipath.conf in their documentation. Nomenclature can be misleading, like active-active, doesn't go far enough to
describe the actual SAN capabilities. In this case a SAN is either Asymmetric Active-Active (AAA) or Symmetric Active-Active (SAA), the former requires the use of ALUA or Asymmetric Logical Unit Access. A good rule thumb is if your array doesn't have Fibre Channel Disks, then it's probably not SAA capable. AAA is also sometimes known as "Dual-Active".
- Explination of different Multipath arrangements e.g. active-active, active-passive, "dual-active"
- Implict/Explicit ALUA article, focused on Solaris but relevant to all platforms
NOTE: AAA arrays usually report path states of active/passive or active/ghost
