User guide
© DataDirect Networks 2011. Multipath (V1.8) User Guide | 17
# multipath -ll
mpath19 (360001ff0721160000000002688e10002) dm-2 DDN,S2A 6620
[size=21T][features=1 queue_if_no_path][hwhandler=0][rw]
\_ round-robin 0 [prio=50][active]
\_ 1:0:0:2 sdg 8:96 [active][ready]
\_ round-robin 0 [prio=10][enabled]
\_ 2:0:0:2 sdf 8:80 [active][ready]
First Path on Path Group 1 (could be more than one)
\_ 1:0:0:2 sdg 8:96 [active][ready]
^ ^ ^ ^ ^
| | | | |________ Physical Path State
| | | |______________ DM Path State
| | |____________________ Device Major/Minor Numbers
| |________________________ Block Device Name
|_____________________________ SCSI Path Info, host:channel:scsi id:LUN
The Path State refers to the physical state of a path. There are currently 4 states in which a
path can be. The “ready” state means the path is available to handle IO requests. A “faulty”
state means the path is currently down and cannot handle IO requests. A “shaky” state means
the path is available, but for some reason is not capable of handling IO requests. The “ghost”
state is a passive path in an “active-passive” arrangement.
The device mapper path state is the multipath kernel module’s state of a path. An “active”
status means that the last IO requested through this path completed without incidence. A
“failed” status means that the last IO requested down the path did not complete and failed.
The device Major/Minor numbers are assigned by the Linux kernel and are used to read/write
to the device file itself. The major number refers to the device driver type and the minor
number refers to the unique device within the device driver type.
Block Device names are used to address the Major/Minor devices. The sdg (in the example
above) refers to a SCSI device driver type (sd) and the enumerated, unique device of this type
(g).
SCSI Path Information displays the specific attributes of the path to the device. There are four
comma separated attributes; host, channel, SCSI id, and LUN id. The host attribute refers to the
initiator (Fibre Channel or Infiniband) port within the server. The channel and SCSI id attributes
are set within the HBA/HCA interface. The LUN id displays the LUN number of the SCSI device
from the presented target device.