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RE: [dm-devel] Multipath on boot and root partition with Redhat5.0



I use multipath boot (/boot) and root (/) on SLES9 kernel 2.6.5 on IBM
mainframe Linux with scsi LUNs. I'm not familiar with redhat5 or HP, but
from your post I guess it's newer kernel and newer multipath-tools than
my SLES9.
I did a howto for SLES9
http://www.linuxvm.org/Info/HOWTOs/root-on-multipath.html
but probably won't help you other than hinting at a way; many
differences in our two linux systems.

SLES 10 (kernel 2.6.16?) says it supports root-on-multipath (not boot
though), may be a common feature with redhat 5 too?

As you said, "on boot the multipath.conf file is not read", so that
maybe explains your mpath0 has defaulted alias name when you really
wanted the persistent name to be os_lun as per your multipath.conf. And
the fstab LABEL='s get you around that unexpected mpath0 device name.

General idea is to modify the initial ramfs /init script to run
multipath early; put your current multipath.conf in the initramfs cpio
archive so your aliases are used.  Note that though I have a
multipath-ed /boot after multipath runs, I boot from any single one of
its available paths; mainframe boot loader's not aware of the multiple
paths.
 
good luck


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-----Original Message-----

From: dm-devel-bounces redhat com [mailto:dm-devel-bounces redhat com]
On Behalf Of Sandrine Twardy
Sent: Wednesday, October 10, 2007 6:59 AM
To: dm-devel redhat com
Subject: [dm-devel] Multipath on boot and root partition with Redhat5.0

Hello,

I have a SAN Eva 5000 HP And I have installed a redhat 5.0 on my server 
with "linux mpath", so far all is fine.
I have an os device multipathed as follow :

 > multipath -ll
mpath0 () dm-0 COMPAQ,HSV110 (C)COMPAQ
[size=7.0G][features=0][hwhandler=0]
\_ round-robin 0 [prio=0][active]
\_ 3:0:0:1 sdb 8:16  [active][ready]
\_ 4:0:0:1 sdc 8:32  [active][ready]

But when I presents a new lun to my host and scans again the scsi lun, I

am losing the multipath on the disk (/ and /boot)
(possibly because the name of device is changed from sdb/sdc to sdc/sde
? )

Here's an extract of my multipath.conf:

multipath {
              wwid                    3600508b40000c1c50001c000000b0000
              path_grouping_policy    group_by_serial
              rr_weight               uniform
              prio_callout            /bin/true
              alias                   os_lun
      }
     But it's seems that on boot the mutlipath.conf file is not read.  
Am I right?
When the system is booted, multipathd cannot use the boot device ...
What can I do to fix the boot device name persistence? Where is supposed

to be configuration file that defines the multipath options of the boot 
device ?

Right now, the server can boot because my fstab is like this:
LABEL=/1                /                      LABEL=/boot             
/boot

Thanks you for your help



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