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188 Configuration: Device Mapper Multipath for Linux
Scan for Newly Added Virtual Disks
The rescan_dm_devs command scans the host server system looking for
existing and newly added virtual disks mapped to the host server.
# rescan_dm_devs
If an array virtual disk (VD) is mapped to the host server at a later time the
rescan_dm_devices command must be run again to make the VD a
visible LUN to the operating system.
Display the Multipath Device Topology Using the Multipath Command
The multipath command adds newly scanned and mapped virtual disks to the
Device Mapper tables and creates entries for them in the /dev/mapper
directory on the host server. These devices are the same as any other block
devices in the host.
To list all the multipath devices run the following command.
# multipath –ll
The output should be similar to this example, which shows the output for one
mapped virtual disk.
mpath1 (3600a0b80005ab177000017544a8d6b92) dm-0 DELL,
MD32xxi
[size=5.0G][features=3 queue_if_no_path
pg_init_retries 50][hwhandler=1 rdac][rw]
\_ round-robin 0 [prio=6][active]
\_ 5:0:0:0 sdc 8:32 [active][ready]
\_ round-robin 0 [prio=1][enabled]
\_ 4:0:0:0 sdb 8:16 [active][ghost]
where:
mpath1 is the name of the virtual device created by device mapper. It is
located in the /dev/mapper directory.
DELL is the vendor of the device.
MD3600i is the model of the device.
Sdc is the physical path to the owning controller for the device.
Sdb is the physical path to the non-owning controller for the device.
book.book Page 188 Thursday, December 9, 2010 3:20 PM