[Linux-cluster] Quorum disk over RAID software device

[Thomas Meller]

Just found this thread while searching for illumination.

We are running a self-constructed cluster setup since 4 Years on a 2.4 kernel (RHAS3).
It's a two-machine setup, nothing fancy.
The fancy thing is that we boot the nodes in different computing centers from mirrored SAN devices which are run in separate storage controllers located in different computing centers over twice redundant FC fabrics, set up a mirrored root fs on these and don't need the local disks except for installation.
In short: we survived everything.
:-)

Up to now, we used a vendor-specific multipath software (RDAC), which I want to get rid of. Today we could use RH5.3's dm-multipathing instead.
Quorum is done by usage of Robin Miller's excellent scu utility and some scripting.

To get there, I need to create an initrd which contains:
- the newest qla-drivers
- Qlogic's 'scli' utility
- multipaths set up to create the raid-mirrors on
- mdadm

I am no RedHat-guru and not used to using mkinitrd.
The Qlogic installer creates initrds automatically, but not usable for me.
The mkinird script seems to know md-multipath, but no dm-multipath (as far as I understood it's code).

Currently I am on the local disk, have multipath running, made the qla-drivers and copied scli, mdadm and the needed libraries manually to the initrd.

What do I need in the initrd? I read something of a dm-multipathd.
How can I include all modules needed (which?) by running mkinitrd? (do I need to have multipath and mirrors already running? Are there configfiles to write?)
Is it possible to include specified tools (not modules) in a mkinitrd run?
Why does mdadm -A tell me 'device or ressource busy' on the second of two raid1-devices?

You see, I need the big picture as well as a short intro to mkinitrd and some troubleshooting.
Can anyone help me find my way through? If there's documentation, I will gladly read it first. Up to now, I found only fuzzy things.

Thanks a lot!
Thomas

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