I'm using the native Debian installer in the following example, however, it's
pretty much the same thing for Red Hat and any other distribution out there.
During your installation, the installer will propose a viable partition scheme
for your operating system, instead of accepting the default, choose Manually
Edit Partition Table, and get ready to set up your software RAID.
What you need to do is make sure that the partitions on each hard-drive are
roughly the same size and set the filesystem type as Physical Volume for
RAID on each partition. I usually make one partition on each drive for the
SWAP and one partition for the root partition (/) and mirror each of those.
Then you go to the Configure Software RAID menu option and select
Create New Device (these will be md0 and md1). Choose the two Physical
RAID partitions that you configured for your swap, and then create another
RAID device and choose the two Physical RAID partitions that you configured
for your root mount point (/).
When you go back to the partition list after this, you'll see the RAID devices
that you've created. We now stop working with the actual physical devices and
work solely with md0 and md1, which are basically virtual devices which treat
the mirror as a single device, and can be treated as regular devices. Every
change you make to md0 will be made to both hard-disks mirrored in that
Don't forget to assign your RAID devices mount points. Do this from the main