[lug] more RAID0 on /

D. Stimits stimits at comcast.net
Sat Nov 20 04:49:08 MST 2004

Lee Woodworth wrote:
> 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.

Yes, DM and RAID0 both.

> 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.

The motherboard has integrated U160 SCSI and integrated IDE. All I do is 
change the bios boot setting and it does the right thing. The first 
stage of booting works fine, it reads /boot/ and the error message 
properly names not being able to mount /dev/md0 via major 9, minor 0. 
Anyway, when the BIOS is set to IDE the drive reported as boot by BIOS 
is the IDE, and when it is set to SCSI, it is the SCSI...this system was 
on SCSI for a long time till I ran out of drive and did the FC2 install 
to IDE so I wouldn't lose what I had...then I copied over what needed to 
be backed up to the IDE, and wiped the SCSI clean and have been 
experimenting with RAID0 since then. Back when I did this with XFS 
filesystem before the stock kernel supported it, I did this same thing 
and I had kept the IDE install for a long time as a rescue disk.

> 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.

I used raidtools via mkraid. If I boot to the IDE drive and have 
/dev/md0 in fstab it autodetects and mounts it fine. The exact same 
kernel and initrd fails when md0 is the root device, but if I rescue 
raidstart I can chroot and it works perfectly. In the case of mkraid the 
raidtab does have persistent-superblock and partition type is linux raid 
autodetect, otherwise it wouldn't succeed in autodetect ever.

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

I'm too tired to do this right now, but I think this is the way to 
go...if I can find the right kernel parameters without using raidstart 
it might work.

> 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.

I was unable to get knoppix to run md0 but at the time I don't think I 
had tried raidstart. I do recall the /proc/ showed an empty mdstat 
though. The KRUD install disk in rescue mode is what I had most success 
with, but again I had to use raidstart.

D. Stimits, stimits AT comcast DOT net

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