Multipath -ll command output in detail

The multipath -ll command shows the current multipath topology, this includes information regarding which path is active, how the paths are grouped, and how the meta-devices will behave in case of a complete path loss

Sample Output is given below

-----------------------------------------------------------------------------------------------------------------------

    diskname (360014380056efd060000d00000510000) dm-3 Vendor,StorageModel

    [size=1.0G][features=1 queue_if_no_path][hwhandler=0][rw]

    \_ round-robin 0 [prio=100][active]

     \_ 0:0:0:1 sda 8:0   [active][ready]

     \_ 1:0:1:1 sdd 8:48  [active][ready]

    \_ round-robin 0 [prio=20][enabled]

     \_ 0:0:1:1 sdb 8:16  [active][ready]

     \_ 1:0:0:1 sdc 8:32  [active][ready]

-----------------------------------------------------------------------------------------------------------------------

Each multipath device is defined using the following format:

-----------------------------------------------------------------------------------------------------------------------

    action_if_any: alias (wwid_if_different_from_alias)
    [size][features][hardware_handler]

------------------------------------------------------------------------------- 

Where:

• action_if_any: If multipath is performing an action, while running the command this action will be displayed here. An action can be "reload", "create" or "switchpg"
• alias: is the name of the multipath device as can be found under /dev/mapper/
• wwid_if_different_from_alias: is the scsi wwid, the unique identifier of the LUN
• size: is the size of the multipath devices
• features: is a list of all the options enabled for this multipath device (e.g. queue_if_no_path)
• hardware_handler: This is 0 if no hardware handler is in use. This is 1 and the name of the hardware handler kernel module in use.

For each path group:

---------------------------------------------------------------------------------------------------------------------- 

\_ scheduling_policy [path_group_priority_if_known] [path_group_status_if_known]

-------------------------------------------------------------------------------

for example:

----------------------------------------------------------------------------------------------------------------------

    \_ round-robin 0 [prio=100][active]

-------------------------------------------------------------------------------

Where:

• scheduling_policy: is the path selector algorithm in use for this path group
• path_group_priority_if_known: Each path can have a priority assigned to it by a callout program. Path priorities can be used to group paths by priority and change their relative weights for the algorithm that defines the scheduling policy.
• path_group_status_if_known: The status of the path can be one of the following:
• active - Path group currently receiving I/O requests.
• enabled - Path groups to try if the active path group has no paths in the ready state.
• disabled - Path groups to try if the active path group and all enabled path groups have no paths in the active state.

For each path:

---------------------------------------------------------------------------------------------------------------------------

    \_ host:channel:id:lun devnode major:minor [dm_status_if_known] [path_status]

----------------------------------------------------------------------------------

for example:

---------------------------------------------------------------------------------------------------------------------------

    \_ 5:0:0:1 sdk 8:160 [active][ready]

----------------------------------------------------------------------------------

Where:

• host:channel:id:lun: are the SCSI host, channel, id and lun values that identify the LUN
• devnode: is the name of the device
• major:minor: the major and minor number of the block device
• dm_status_if_known: Is similiar to the path status, but from the  kernel's point of view. The dm status has two states: "failed", which is  analogous to "faulty", and "active" which covers all other path states.
• path_status: the status of the path can be one of the following:
• ready - Path is able to handle I/O requests.
• shaky - Path is up, but temporarily not available for normal operations.
• faulty - Path is unable to handle I/O requests.
• ghost - Path is a passive path, on an active/passive controller.
• dm_status_if_known: Is similiar to the path status, but from the kernel's point of view. The dm status has two states:
• failed - which is analogous to "faulty", and
• active - which covers all other path states.