Re: [SLUG] Adding RAID to Linux *after* installation?

[Jeff Waugh <jdub@xxxxxxxxxxxxxx>]

<quote who="lukekendall@xxxxxxxxxxxxxxxx">

>   mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hda7 /dev/sda7
> 
> it refuses, as /dev/hda7 ("/") is mounted.

Okay, so do this instead:

  mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sda7 missing

That will create a 2 device array with one missing device. You need to bring
up the array (watch /proc/mdstat to see its status), mount it, then copy
over everything from / (using cp -a or similar). Now set up everything in
the copied partition to boot from /dev/md0 instead of /dev/hda7, and then
reboot. Boot from /dev/hda0 by using the grub menus (if you've made sure
they're changed), or edit the boot command line to do it manually. You
should find yourself running a system with / on /dev/md0. At this point, you
can use mdadm to add /dev/sda7 to the array - after checking everything is
okay, of course! :-)

This is not a wildly uncommon thing to do, but it's so easy to install with
RAID now that I think most people just do that.

> Obviously I should try this on the /home partition, not slash, until I get
> the steps worked out.  At least that way if I lose any data, it'll be a
> tiny amount of junk instead of 10GB of carefully setup Linux system!

That's a good idea. :-) Running an array reliably on / or /boot requires
some extra work anyway.

- Jeff

-- 
linux.conf.au 2007: Sydney, Australia           http://lca2007.linux.org.au/
 
   I don't know whose brain child it was, but it was quite an ugly child.