If you run most any type of services in a production environment, chances are, you want some sort of redundancy and load balancing. As an example, if you're running a web site, you want that to be up as much as possible, so generally a load balancer is used to send the load between different web servers. A common load balancer used is a big-ip F5. These have a great configuration tool and work very well, but they're also very expensive.

In order to create a raid-5 set in Linux, you can do the following:

1. Create partitions using fdisk or parted on your disks. For Raid-5, you need at least 3. If you create the partitions with the type of 0xfd, you don't need to create a mdadm.conf file. mdadm -A -s is ran on system startup and automagically finds these things.
2. mdadm --create /dev/md0 --chunk=128 --level=5 --raid-devices=5 /dev/sd[b,c,d,e,f]1

3. Add the following lines to /etc/mdadm.conf:

DEVICE /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1 /dev/sdf1

I haven't done much with LVM in Linux. In Red Hat 4, it became possible to use it to manage your volumes. In Red Hat 5, it's the default method for dealing with disks. I've done a fair amount with Veritas Volume Manager (VxVM) under Solaris, however, it's been awhile. But, the concepts I learned under VxVM are similar to that of the Linux LVM.

One thing that appears to be different about Linux LVM vs VxVM is that LVM only creates raid 0/1 sets and NOT raid 5 sets. If you need Raid 5, you have to use a md device.However, md sets can create 0/1/5 raid sets.