---

At this post, I will add a brief explanation of "how to configure RHEL native multipath(device-mapper-multipath) for EMC storage".

Environment:

• Red Hat Enterprise Linux 6-7
• device-mapper-multipath (DM-Multipath)
• ECM  Clariion/VNX/Unity

Resolution: 

Multiple LUNs for RHEL 6.0 and later

Step 1: Check installed  HBA modules  with  lspci

#yum install -y pciutils

# lspci |grep -i fibr
07:00.0 Fibre Channel: QLogic Corp. ISP2532-based 8Gb Fibre Channel to PCI Express HBA (rev 02)
0a:00.0 Fibre Channel: QLogic Corp. ISP2532-based 8Gb Fibre Channel to PCI Express HBA (rev 02)

Step 2:  Configure grub.conf

Add scsi_mod.max_report_luns and  scsi_mod.max_luns to 'kernel' line  in  /etc/grub.conf and reboot system.

kernel /vmlinuz-2.6.32-573.12.1.el6.x86_64 ro root=/dev/mapper/vgroot-lvroot rd_NO_LUKS  KEYBOARDTYPE=pc KEYTABLE=trq LANG=en_US.UTF-8 rd_NO_MD rd_LVM_LV=vgroot/lvswap SYSFONT=latarcyrheb-sun16 crashkernel=128M rd_LVM_LV=vgroot/lvroot rd_NO_DM rhgb quiet  scsi_mod.max_report_luns=32768 scsi_mod.max_luns=32768

Step 3: Configure  multipath.conf  file

**Please check EMC Host Connectivity Guide for Linux for multipath configuration on  page  194-207. I added a  simple configuration sets  for  RHEL6.x and  RHEL7.x . But don't forget to check your RHEL subversion  to find out spesific config sets. For example  RHEL 6.5  supports ALUA option. So maybe  you need to configure  multipathd  with  ALUA options. And also  RHEL 7.2 and  later has an option  "retain_attached_hw_handler" that can recognize PNR and ALUA automatically and does not need changes to the multipath.conf file.

## Use user friendly names, instead of using WWIDs as names.
defaults {
user_friendly_names yes
}
blacklist {
devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
devnode "^hd[a-z]"
devnode "^cciss!c[0-9]d[0-9]*"
}
devices {
device {
vendor "DGC"
product ".*"
product_blacklist "LUNZ"
path_grouping_policy group_by_prio
getuid_callout "/lib/udev/scsi_id --whitelisted --device=/dev/%n"
path_checker emc_clariion
features "1 queue_if_no_path"
hardware_handler "1 emc"
prio emc
failback immediate
rr_weight uniform
no_path_retry 60
}
}

Multiple LUNs for RHEL 7.0 and later

Step 1: Check installed  HBA modules  with  lspci

#yum install -y pciutils
# lspci |grep -i fibr
07:00.0 Fibre Channel: QLogic Corp. ISP2532-based 8Gb Fibre Channel to PCI Express HBA (rev 02)
0a:00.0 Fibre Channel: QLogic Corp. ISP2532-based 8Gb Fibre Channel to PCI Express HBA (rev 02)

*So I'll follow to define a configuration for  QLogic. If you have an Emulex adapter and then check EMC Host Connectivity Guide for Linux.

Step 2:  Configure grub.conf

Add scsi_mod.max_report_luns and  scsi_mod.max_luns to grub.conf

# cat /etc/default/grub
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=vgroot/lvroot rhgb quiet scsi_mod.max_report_luns=32768 scsi_mod.max_luns=32768"
GRUB_DISABLE_RECOVERY="true"

Step 3: Mkconfig  for  Grub

#grub2-mkconfig -o /boot/grub2.cfg
#dracut -f
#reboot

Step 4: Configure multipath.conf  file

*Since RHEL7.2, the default stanza parameter retain_attached_hw_handler yes can recognize PNR and ALUA automatically and does not need changes to the multipath.conf file. However, the manual configuration of PNR and ALUA will still work.

defaults {
user_friendly_names yes
find_multipaths yes
}
blacklist {
}
devices {
device {
vendor "DGC"
product ".*"
product_blacklist "LUNZ"
path_grouping_policy "group_by_prio"
path_checker "emc_clariion"
features "1 queue_if_no_path"
hardware_handler "1 emc"
prio "emc"
failback immediate
rr_weight "uniform"
no_path_retry 60
retain_attached_hw_handler yes
detect_prio yes
}
}
multipaths {
}