Configuration: Device Mapper Multipath for Linux 197
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)
• I/O may hang when a Device Mapper device is deleted before the volume
is unmounted.
• If the scsi_dh_rdac module is not included in initrd, slower device
discovery may be seen and the syslog may become populated with buffer
I/O error messages.
• I/O may hang if the host server or storage array is rebooted while I/O is
active. All I/O to the storage array must be stopped before shutting down
or rebooting the host server or storage array.
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.
Table 14-1. Useful Device Mapper Commands
(continued)
Command Descriptions
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