[CentOS] Multipath-root (mpath) problems with CentOS 5

Sun Apr 15 17:36:40 UTC 2007
Finnur Örn Guðmundsson <finnzi at finnzi.com>

Pasi Kärkkäinen wrote:
> Hi list!
>
> I have a server with dual port Qlogic iSCSI HBA. I set up the same LUN for
> both ports, and boot the CentOS installer with "linux mpath". 
>
> Installer detects multipathing fine, and creates mpath0 device for root disk.
> Installation goes fine, and the system boots up and works fine after the
> install from the multipath root device.
>
> After install the setup is like this:
>
> LUN 0 on port 1: /dev/sda
> LUN 0 on port 2: /dev/sdb
>
> and those form mpath0 device, which works OK.
>
> But then comes the problem.. when I add another LUN for both ports, the
> setup is like this:
>
> LUN 0 on port 1: /dev/sda
> LUN 1 in port 1: /dev/sdb
>
> LUN 0 on port 2: /dev/sdc
> LUN 1 on port 2: /dev/sdd
>
> And now after rebooting the system, root device multipath (mpath0) doesn't
> work anymore.. initrd seems to use/mount /dev/sda* partitions instead of mpath0
> device. In fact the whole mpath0 is not started up.
>
> The weird thing is that the other LUN is now using multipathing instead.. 
> using mpath1 device. 
>
> How can I fix that? I'd like to use multipathing for both LUNs, also for root
> device.  
>
> If I regenerate initrd with verbose flag, it just sets up the mpath1, not
> mpath0. I guess that's because mpath0 is not running when regenerating
> initrd. 
>
> I have edited /etc/multipath.conf and disabled the "blacklist" line, and
> added multipath-entries for both LUNs. So those should be fine..
>
> Any ideas? 
>
> Thanks!
>
> -- Pasi
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>   
There seems to be a bug in the upstream version with mpath & root 
devices.....I asked RedHat support to help me with a similar problem but 
go the answer that i should wait until update 1....the current 
implementation of mpath for boot devices seems to handle adding 
paths/devices somewhat weird if you add/remove paths....

Bgrds,
Finnur