Linux: Native Multipath Configration on RHEL 4

1. The device-mapper-multipath package is not installed as part of a default installation of the operating system. Select the package as part of the OS install or install the rpm later either from the install CD or by downloading the rpm from the Red Hat website.
2. Verify that the required version of uDev has been installed for your environment. To query the uDev version, execute the command:

# rpm -q udev
If required, upgrade the uDev package and then execute the
command to create a new device under the ‘/dev’ directory.

# udevstart
3. Load the dm_multipath kernel module if it is not already loaded.

# modprobe dm_multipath
4. Replace the default /etc/multipath.conf with the following multipath.conf file recommended by EMC for attach to EMC storage.

Follow the instructions in the annotated multipath.conf file for masking internal scsi disks or disks that need to be excluded from multipath control.

## This is the /etc/multipath.conf file recommended for
## EMC storage devices.
##
## OS : RHEL 4 U3
## Arrays : CLARiiON and Symmetrix
##
## The blacklist is the enumeration of all devices that are to be
## excluded from multipath control
devnode_blacklist
{
## Replace the wwid with the output of the command
## ‘scsi_id -g -u -s /block/[internal scsi disk name]’
## Enumerate the wwid for all internal scsi disks.
## Optionally, the wwid of VCM database may also be listed here.
##

wwid 35005076718 d4224d
devnode “^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*”
devnode “^hd[a-z][0-9]*”
devnode “^cciss!c[0-9]d[0-9]*[p[0-9]*]”
}
## Use user friendly names, instead of using WWIDs as names.
defaults {
## Use user friendly names, instead of using WWIDs as names.
user_friendly_names yes
}
devices {
## Device attributes requirements for EMC Symmetrix
## are part of the default definitions and do not require separate
## definition.
## Device attributes for EMC CLARiiON
device {
vendor “DGC “
product “*”
path_grouping_policy group_by_prio
getuid_callout “/sbin/scsi_id -g -u -s /block/%n”
prio_callout “/sbin/mpath_prio_emc /dev/%n”
path_checker emc_clariion
path_selector “round-robin 0”
features “1 queue_if_no_path”
no_path_retry 300
hardware_handler “1 emc”
failback immediate
}
}
5. Perform a dry run and evaluate the setup by running the
following command.
# multipath -v2 -d
• With Symmetrix Logical Units, the output will look similar to:
create: SEMC_____SYMMETRIX______490073232000
[size=5 GB][features=”0″][hwhandler=”0″]
_ round-robin 0
_ 11:0:1:52 sdao 66:128
_ 11:0:2:52 sdaz 67:48
_ 10:0:1:52 sdm 8:192
_ 10:0:2:52 sdx 65:112
create: SEMC_____SYMMETRIX______490073233000
[size=5 GB][features=”0″][hwhandler=”0″]
_ round-robin 0
_ 11:0:1:53 sdap 66:144
_ 11:0:2:53 sdba 67:64
_ 10:0:1:53 sdn 8:208
_ 10:0:2:53 sdy 65:128
create: SEMC_____SYMMETRIX______490073234000
[size=5 GB][features=”0″][hwhandler=”0″]
_ round-robin 0
_ 11:0:1:54 sdaq 66:160
_ 11:0:2:54 sdbb 67:80
_ 10:0:1:54 sdo 8:224
_ 10:0:2:54 sdz 65:144
• With CLARiiON Logical Units, the output will look similar to:
create: 360060160b540160171f77f705558da11
[size=10 GB][features=”1
queue_if_no_path”][hwhandler=”1 emc”]
_ round-robin 0
_ 11:0:0:0 sdad 65:208
_ round-robin 0
_ 10:0:0:0 sdb 8:16
create: 360060160b540160170f77f705558da11
[size=10 GB][features=”1
queue_if_no_path”][hwhandler=”1 emc”]
_ round-robin 0
_ 11:0:0:1 sdae 65:224
_ round-robin 0
_ 10:0:0:1 sdc 8:32

6. If the listing is appropriate, commit the configuration as follows:
a. Start the required multipath processes.

# /etc/init.d/multipathd start
b. Execute the multipath command.

# multipath -v2
c. Perform an ‘lsmod’ and verify that the processes are running.

• With Symmetrix attach the following modules should be listed:
# lsmod |grep dm
dm_round_robin 4929 1
dm_multipath 22097 2 dm_round_robin
dm_mod 66433 1 dm_multipath

• With CLARiiON attach the following modules will be listed:

dm_emc 7489 1
dm_round_robin 4929 1
dm_multipath 22097 3 dm_emc,dm_round_robin
dm_mod 66433 3 dm_multipath

7. To get a listing of the current setup do:

# multipath -ll
8. Integrate the startup of the appropriate daemons in the boot sequence as follows:

# chkconfig --add multipathd
# chkconfig multipathd on

9. Device-mapper (dm) names and sd device names may not be persistent across reboots. There are two mechanisms to achieve persistence:

• Use of friendly names.
The friendly names are softlinks created in the /dev/mpath/ directory.

• Use of LVM-2 on top of device-mapper Configure logical volumes as necessary. LVM based entries in ‘/etc/fstab’ are supported. In the normal boot process, the device mapper and the multipath daemons start before LVM starts the discovery process.

You may optionally reboot the host to verify that the required processes automatically startup.

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