Setting up SAN boot for RHEL 6.x using native multipath on EMC storage

Published 14 Mar 2014 Read time 2 min(s) 42 sec(s) (2523 views). Linux

You can set up a SAN boot LUN to work in a Red Hat Enterprise Linux environment that is using the FC protocol. This article specifically looks at RHEL 6.x but the procedure will work with RHEL 5.x environments

Before you begin

Verify that your system setup supports SAN boot LUNs
You are running RHEL 6.x (see bottom of article for 5.x details)
EMC storage setup with Active/Active (ALUA)
Boot lun was presented with single path for initial install

Procedure:

Server boots up after initial install

[root@server1]# mpathconf --enable —-with_multipathd y

Edit /etc/multipath.conf and make sure it only contains following valid parameters

blacklist {
}
defaults {
  user_friendly_names yes
}
devices {
  device {
    vendor "DGC"
    product ".*"
    product_blacklist "LUNZ"
    hardware_handler "1 alua"   
    path_checker directio    
    prio alua                
  }
}

Find out the logical path the root disk is mapped
```
[root@server1]# multipath —v3
```
It should be /dev/mapper/mpatha

Create initramfs with multipath module

[root@server1]# dracut --force -—add multipath

Make sure multipath.conf is included in initrd image

[root@server1]# lsinitrd /boot/initramfs-*.x86_64.img | grep multipath.conf
-rw-r--r--   1 root     root         2525 Feb 27 13:31 etc/multipath.conf

Modify the /boot/grub/device.map and change
```
(hd0) /dev/sda
```
to
```
(hd0) /dev/mapper/mpatha
```
This is assuming the boot disk is on /dev/mapper/mpatha as verified in step 2 above.
Reboot the server.

Verify multipath, check hwhandler='1 alua' and member disk sda for mpatha

[root@server1]# multipath —ll 
mpatha (3600601609973310067eb1e1ed69ae311) dm-0 DGC,VRAID
size=150G features='1 queue_if_no_path' hwhandler='1 alua' wp=rw
`-+- policy='round-robin 0' prio=10 status=enabled
  |- 1:0:0:0 sda 8:0   active ready running

Ask storage administrator to enable other paths for boot LUN.
Reboot server again after multipath is aenabled in storage too

hwhandler='1 alua' prio>0

If hwhandler='1 emc' or prio=0 means PNR mode

[root@server1]# multipath -ll
mpatha (3600601609973310067eb1e1ed69ae311) dm-0 DGC,VRAID
size=150G features='1 queue_if_no_path' hwhandler='1 alua' wp=rw
|-+- policy='round-robin 0' prio=130 status=active
| |- 1:0:1:0 sdd 8:48  active ready running
| `- 2:0:1:0 sdj 8:144 active ready running
`-+- policy='round-robin 0' prio=10 status=enabled
  |- 1:0:0:0 sda 8:0   active ready running
  `- 2:0:0:0 sdg 8:96  active ready running
mpathb (360060160997331009fd6e124d69ae311) dm-1 DGC,VRAID
size=800G features='1 queue_if_no_path' hwhandler='1 alua' wp=rw
|-+- policy='round-robin 0' prio=130 status=active
| |- 1:0:0:1 sdb 8:16  active ready running
| `- 2:0:0:1 sdh 8:112 active ready running
`-+- policy='round-robin 0' prio=10 status=enabled
  |- 1:0:1:1 sde 8:64  active ready running
  `- 2:0:1:1 sdk 8:160 active ready running

Partition other LUNS using fdisk command as normal, but use logical path /dev/mapper/mpathb etc (partition will be created as /dev/mapper/mpathbp1 instead of /dev/mapper/mpathb1 NOTE: any change to /etc/multipath.conf requires re-create initramfs ( dracut --force -—add multipath) and a reboot, because the boot LUN is on SAN, if boot LUN is local disk, change to /etc/multipath.conf only requires multipathd restart

RHEL 5.x

You can also apply this procedure to RHEL 5.x based systems. However, for RHEL 5.x use mkinitrd instead of dracut and the /etc/multipath.conf is slightly different.