Using Mdadm; Partitions; Viewing Multipath I/O Status; Section 5.13, "Viewing Multipath I/O Status - Novell LINUX ENTERPRISE SERVER 10 - STORAGE ADMINISTRATION GUIDE 7-2007 Administration Manual

This allows LVM2 to scan only the by-id paths and reject everything else. If you are also using
LVM2 on non-multipathed devices, make the necessary adjustments to suit your setup.

5.12.3 Using mdadm

Just as for LVM2, mdadm requires that the devices be accessed by the UUID rather than by the
device node path. Therefore the DEVICE entry in /etc/mdadm.conf must be modified:
DEVICE /dev/disk/by-id/*

5.12.4 Partitions

Currently, it is not possible to partition multipath I/O devices themselves. If the underlying physical
device is already partitioned, the multipath I/O device reflects those partitions and the layer provides
/dev/disk/by-id/<name>p1 ... pN devices so you can access the partitions through the
multipath I/O layer.
As a consequence, the devices need to be partitioned prior to enabling multipath I/O. If you change
the partitioning in the running system, DM-MPIO does not automatically detect and reflect these
changes. The device must be reinitialized, which usually requires a reboot.

5.13 Viewing Multipath I/O Status

Querying the multipath I/O status outputs the current status of the multipath maps.
The multipath -l option displays the current path status as of the last time that the path checker
was run. It does not trigger the path checker to be run.
The multipath -ll option triggers the path checker, updates the path information, then displays
the current status information. This option always the displays the very latest information about the
path status.
1 At a terminal console prompt, enter
For each device, it shows the device's UUID, size, features, and hardware handlers.
Paths to the device are grouped into priority groups automatically on device discovery. Only one
priority group is active at a time. For an active/active configuration, all paths are in the same group.
For an active/passive configuration, the passive paths are placed in separate priority groups.
54 SLES 10 Storage Administration Guide
multipath -ll
This displays information for each multipathed device. For example:
3600601607cf30e00184589a37a31d911
[size=127 GB][features="0"][hwhandler="1 emc"]
\_ round-robin 0 [active][first]
\_ 1:0:1:2 sdav 66:240
\_ 0:0:1:2 sdr
\_ round-robin 0 [enabled]
\_ 1:0:0:2 sdag 66:0
\_ 0:0:0:2 sdc
[ready ][active]
65:16 [ready ][active]
[ready ][active]
8:32 [ready ][active]