[NTLUG:Discuss] Software RAID-1 success and questions.

[Richard Geoffrion]

From: "Dan Carlson" <dcarlson at dcarlson.net>


> You can use dd if=/dev/zero of=/dev/hdX to erase an entire drive.  It
takes
> a while on a large drive, but it works.
[snip]
>
> If everything is setup properly, swapping hda and hdc should work just
> fine.  In my experience, the only way to know for sure if you have setup
> everything properly is to try it.
[snip
> To have two bootable disks in the same system you can install lilo into
the
> mbr of each disk and use the bios to specify which disk to boot off of.
> This works fine for me.  You will need two separate lilo.conf files (say,
> lilo.conf.hda and lilo.conf hdc) and use the -C option to tell lilo which
> config file to use.  Run lilo twice, once with each config file.  Then try
> changing the boot drive in the bios.  "If everything is setup properly",
it
> should work.
>

I'll have to play around with 'dd' later.

I created an alternate lilo.conf file and pointed the boot device to
/dev/hda.   I reran lilo and was successful in starting the linux system on
either disk.  Which had the side benefit of testing fail-safe recovery on
the RAID array.   Thanks!  It's funny though. I never had to tell lilo to
use /dev/hdb as the boot device.  It seems that it got that information from
/etc/raidtab.  ( I configured /hdc as raid-disk 0.  I assume that since it
was the primary device for /dev/md0, it got the boot loader.  But why not
BOTH disks?  The /boot directories were RAIDed as /dev/md0! )

So far I seem to be doing well, but what about the relationship between
/etc/raidtab and the raid array itself?  Can I update the raidtab file and
change /dev/hda to be raid-disk 0?  What tool causes the RAID system to
re-read the raidtab file and implement the changes?  Does it matter?

And more importantly, what about re-installs on a system on which RAID is
currently setup?  Case and point - Now that I have the desired partitions up
and RAIDed, I am going to do a REAL install of my system.  When I reboot
into the installation will I be able to just mount the /dev/md0 partition?
I'm going to take along my current /etc/raidtab just to be sure, but I hope
I don't have to re-mkraid my partitions.

I suppose I'll post the results of what happens.  I hope no one is getting
bored reading about all my learning.

-Richard