Dell PowerVault MD3200i - Manual (Page 199)

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 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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