184 Configuration: Device Mapper Multipath for Linux
Only multipathing device nodes and partition nodes created using the
directions provided above should be mounted or in any way accessed by the
host system or its users.
Limitations and Known Issues
• In certain error conditions with the no_path_retry or the
queue_if_no_path feature is set, applications may hang. To overcome
these conditions the you must enter the following command for each
affected multipath device:
dmsetup message [device] 0 "fail_if_no_path"
where [device] is the multipath device name (e.g. mpath2; do not specify
the path)
Table 14-1. Useful Device Mapper Commands
Command Descriptions
multipath –h Prints usage information
multipath –ll Displays the current multipath topology using all available
information (sysfs, the device mapper, path checkers, and
so on)
multipath Re-aggregates multipathing device with simplified output.
multipath –f
<multipath_dev_node>
Flushes out Device Mapper for the specified multipathing
device. Used if the underlying physical devices are
deleted/unmapped.
multipath –F Flushes out all unused multipathing device maps.
rescan_dm_devs Dell provided script. Forces a rescan of the host SCSI bus
and aggregates multipathing devices as needed. For use
when:
• LUNs are dynamically mapped to the hosts.
• New targets are added to the host.
• Failback of the storage array is required.
• For MD3200i Series arrays, iSCSI sessions have to be
established for rescan to take effect.
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