Setting up software RAID5 on 2nd, 3rd, and 4th disks

[Bruno Wolff III]

On Wed, Nov 15, 2006 at 08:26:24 -0500,
  James Pifer <jep at obrien-pifer.com> wrote:
> I have a system up and running. I have added three other disks to the
> system that I'd like to setup RAID5 just to have a little bit of
> redundancy. These disks will be used for storage only, so hopefully
> setting up a software RAID won't slow down the system too much. 

Unless you are cpu bound or have a raid controller with battery backed cache
you probably want to use software raid.

> Question is, how do I setup the RAID on these disks after the system
> already has FC5 running? I've done as part of the setup before. I have
> looked at some howto's but they seem pretty old. 

One thing to note is that you normally can't boot off of raid 5 partitions
and you will probably want to use raid 1 for the boot partition.

> Is there a GUI for setting up RAID?

I don't think so, but using mdadm isn't that hard once you know what you
want to do.

Moving stuff around can be a pain though. Software raid uses a small amount
of space at the end of each partition. So you can't just turn an ext3
partition into a software raid partition. (The only case you can do this
is if the file system doesn't use all of the space on the partition and
you are going to use raid 1.)

If you are going to use the current disk as a hot spare for the eventual
raid 5 array, then you could set up the raid 5 array and move stuff over
and then add the old disk as a spare.