I just tried my first install on a box with a Mylex
Acceleraid 200 controller.  The Mylex docs say the driver
supports partitions p1 - p7, i.e. /dev/rd/c0d0p1 through
/dev/rd/c0d0p7.  I tried to install with:
256mb	/
256mb	swap
256mb	/tmp
2000mb	/usr
<remainder>	/var

This is only 5 partitions, yet disk druid created them as
/dev/rd/c0d0p1
/dev/rd/c0d0p5
/dev/rd/c0d0p6
/dev/rd/c0d0p7
/dev/rd/c0d0p8

I don't know why disk druid likes to create just 1 primary
and everything else in an extended partition starting at
partition 5, but it breaks the mylex raid driver.  This
resulted in my /var partition not existing.

I was able to get around this by switching to virtual
console 2, running fdisk by hand, then rebooting and letting
the GUI disk druid use the existing partitions.