The multipath-tools package includes settings for known storage subsystems in a default hardware table, and no additional configuration is required for these devices.
You can specify additional device definitions in /etc/multipath.conf. If the file is present, its content overrides the defaults. You must include the parameters for the storage subsystem that is used either in the default hardware table or in the configuration file. There is no man page available for this file.
Within the multipath-tools package there is a template configuration, see /usr/share/doc/packages/multipathtools/multipath.conf.annotated. This file contains a list of all options with short descriptions.
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