Implementing multipathing with the multipath-tools
The multipath-tools project is an open source project that implements I/O multipathing at the operating system level.
The project delivers an architecture and vendor-independent multipathing
solution that is based on kernel components and the following user-space
tools:
- The kernel device-mapper module (dm_multipath)
- The hotplug kernel subsystem
- The device-naming tool udev
- The user-space configuration tool multipath
- The user-space daemon multipathd
- The user-space configuration tool kpartx to create device maps from partition tables
Redundant paths that are defined in Linux® appear as separate SCSI devices, one for each logical path (see Figure 1). The device-mapper provides a single block device for each logical unit (LU) and reroutes I/O over the available paths. You can partition the device-mapper multipath I/O (MPIO) devices or use them as physical volumes for LVM or software RAID.
You can use user-space components to set up the MPIO devices and
automated path retesting as follows:
- Use the multipath command to detect multiple paths to devices. It configures, lists, and removes MPIO devices.
- Use the multipathd daemon to monitor paths. The daemon tests MPIO devices for path failures and reactivates paths if they become available again.
Figure 1 shows an example multipath setup with two FCP channels for the mainframe and two HBAs for the storage subsystem.
