[lug] more RAID0 on /

Lee Woodworth blug-mail at duboulder.com
Sat Nov 20 01:36:53 MST 2004

Its been a while since I fiddled with the soft-raid, so this may not 
apply to your situation at all.

Presumably you have the device mapper compiled into the kernel.

You didn't say whether you are unplugging the IDE drives when you are 
switching from IDE to SCSI mode. If the IDEs are still present, they 
could affect what is considered /dev/md0.

Did you prepare the SCSI raid using mdadm or raidtools? raidtools is 
more dependent on a config file than mdadm. mdadm creates super-blocks 
on the raid partitions for defining the arrays and the kernel md driver 
uses them during startup.

See man 4 md for kernel parameters related to defining md devices manually.

If the kernel params don't help, try booting a live-cd (e.g. knoppix) 
that has the device mapper kernel module and then look at /proc/mdstat 
to see what the md driver found during boot.

D. Stimits wrote:
> Ok, with some hints from people here I've partially solved the dilemma. 
> At this point I was able to use rescue mode and install grub on the scsi 
> part of the system (review: installed to IDE and trying to swap over to 
> SCSI with RAID0 root partition, and normal SCSI /boot/), and get it 
> partially working.
> At this point it reads the kernel off the /boot/ partition, and gets as 
> far as attempting pivot_root, then fails. Now since the kernel has raid0 
> compiled in directly, I am guessing that it is failing to raidstart 
> /dev/md0. The partitions are marked in fdisk as "Linux raid autodetect" 
> though, and if I boot to this same kernel (it is an exact copy) under 
> IDE it does automatically detect and start /dev/md0. My question is why 
> if this is autostart raid0, how come it works under IDE but not under 
> SCSI with root partition on md0? Does autodetect require something that 
> must be made available by mounting the root partition, thus defeating 
> the ability to raidstart? Or should the kernel with compiled in RAID0 
> and autodetect marked partitions detect properly to allow mount of 
> /dev/md0 on /? Or perhaps my grub.conf kernel line is incorrect:
>    kernel /vmlinuz-2.6.9-2smp ro root=/dev/md0
> Unless there is something in init to raidstart autodetect that is itself 
> initially stored and loaded from "/", I can't see a reason why this 
> would fail. Hints or clues? Do I have to custom build initrd differently 
> when root partition is RAID0 in order to raidstart despite autodetect?
> D. Stimits, stimits AT comcast DOT net
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