Device-Mapper Multipath (DM-Multipath) is a native Linux multipath tool that allows you to configure multiple I/O paths between a server and a storage device into a single path. Multiple paths to storage devices provide redundancy and failover capabilities, as well as improved performance and load balancing.
DM-Multipath can be configured in either of the following configurations:
- Active/Passive (or Standby) – Only half the paths are used for I/O. If any component in the active path fails, DM-Multipath switches I/O to the alternate path.
- Active/Active – In an active/active configuration, DM-Multipath can be configured to spread the I/O load across all paths in a round-robin fashion or can dynamically balance the load.
The slide shows a simple DM-Multipath configuration through a storage area network (SAN). There are two I/O paths in this example:
- Host bus adapter (hba1), through the SAN, to Controller (ctrl1)
- Host bus adapter (hba2), through the SAN, to Controller (ctrl2)
Without DM-Multipath, each I/O path is a separate device even though the path connects the same server to the same storage device. DM-Multipath creates a single multipath device on top of the underlying devices.
To enable the DM-Multipath services on your system, install the device-mapper-multipath software package from the ol8_baseos_latest repository:
# dnf install device-mapper-multipath
When installing the device-mapper-multipath package, dnf also installs device-mapper-multipath-libs as a dependency package. The packages install several files, including the following:
- /usr/sbin/multipath – Device mapper target auto-configurator that is used to detect and configure multiple paths to devices
- /usr/sbin/multipathd – Multipath daemon that checks for failed paths and reconfigures the multipath map to regain connectivity. This daemon executes /usr/sbin/multipath when events occur.
- /usr/sbin/mpathconf – Utility for configuring device-mapper-multipath. It creates or modifies multipath.conf and is also used to display the current status.
Several files and directories are installed, including:
/usr/sbin/multipath Utility that detects and configures multiple paths to devices
/usr/sbin/multipathd DM-Multipath daemon
/usr/sbin/mpathconf Utility for configuring DM-Multipath
Man pages are also installed for multipath(8), multipathd(8), multipath.conf(5), and mpathconf(8).