1.4. DM Multipath components

Component

Description

dm_multipath kernel module

Reroutes I/O and supports failover for paths and path groups.

mpathconf utility

Configures and enables device mapper multipathing.

multipath command

Lists and configures the multipath devices. It is also executed by udev whenever a block device is added, to determine if the device should be part of a multipath device or not.

multipathd daemon

Automatically creates and removes multipath devices and monitors paths; as paths fail and come back, it may update the multipath device. Allows interactive changes to multipath devices. Reload the service if there are any changes to the /etc/multipath.conf file.

kpartx command

Creates device mapper devices for the partitions on a device. This command is automatically executed by udev when multipath devices are created to create partition devices on top of them. The kpartx command is provided in its own package, but the device-mapper-multipath package depends on it.

mpathpersist

Sets up SCSI-3 persistent reservations on multipath devices. This command works similarly to the way sg_persist works for SCSI devices that are not multipathed, but it handles setting persistent reservations on all paths of a multipath device. It coordinates with multipathd to ensure that the reservations are set up correctly on paths that are added later. To use this functionality, the reservation_key attribute must be defined in the /etc/multipath.conf file. Otherwise the multipathd daemon will not check for persistent reservations for newly discovered paths or reinstated paths.