HP 3PAR RedHat and Oracle Linux Implementation Guide

9 Modifying HP 3PAR Devices on the Host
Creating Device-mapper Devices
Complete the following steps to create Device-mapper devices.
1. Run the multipath command to create new Device-mapper nodes under the /dev/mapper
directory.
# multipath
2. Verify that the Device-mapper devices have been created by issuing multipath -11.
For example, in the following RHEL 4 host output, the /dev/mapper/350002ac0000c003e
Device-mapper node is seen from device sda on driver instance (0:0:0:0) and from sdb on
driver instance (1:0:0:0).
NOTE: RHEL 5.5 and later, including RHEL 6.x, have the user_friendly_names option
for dm multipathing turned on by default. This means that instead of device names like
350002ac001b40031 they will appear as mpathX, giving paths of /dev/mapper/mpathX
in kpartx and other tools as per the RHEL documentation.
# multipath -ll
350002ac001b40031
[size=5 GB][features="1 queue_if_no_path"][hwhandler="0"]
\_ round-robin 0 [active]
\_ 0:0:0:0 sda 8:0 [active][ready]
\_ 1:0:0:0 sdb 8:16 [active][ready]
3. After creating the devices, use the multipath -v 3 command to retrieve more detailed
information about Device-mapper nodes and their associated paths. Make sure of the following
settings:
• The path checker is set to tur for each of the devices.
• The no_path_retry is set to a value of 12 for iSCSI and 18 for Fibre Channel if the
HP 3PAR array is running HP 3PAR OS 3.1.1 or later. However, if the HP 3PAR array is
running an HP 3PAR OS version earlier than 3.1.1, then the no_path_retry is set to
12 for iSCSI and 12 for Fibre Channel.
Output from the multipath -v 3 command differs in RHEL 4 on the one hand and RHEL
6 or RHEL 5 on the other; however, the information displayed on the Device-mapper remains
the same.
Example using RHEL 5:
# multipath -v 3
sdc: not found in pathvec
sdc: mask = 0x1f
sdc: bus = 1
sdc: dev_t = 8:32
sdc: size = 10485760
sdc: vendor = 3PARdata
sdc: product = VV
sdc: rev = 0000
sdc: h:b:t:l = 2:0:0:0
sdc: serial = 004B0079
sdc: path checker = tur (controller setting)
sdc: state = 2
Creating Device-mapper Devices 115