I have a system with an onboard Promise FastTrack SATA RAID controller. This isn't a "real" RAID controller, but one which relies on the OS to perform some of the RAID work. This is commonly called "FakeRAID" and is not desirable.
Despite setting the controller into AHCI Mode in the BIOS, I still get a disk called /dev/mapper/pdc_abcdef or similar and cannot use the disk /dev/sdb directly. I wanted the FakeRAID gone.
The FakeRAID is managed by Device-Mapper RAID called "dmraid".
An old CentOS 5 post
suggests removing the dmraid package might work, but this wanted to
remove anaconda and many other things, so didn't seem a good option.
There is a kernel boot parameter to disable Device-Mapper RAID so I applied this.
In /etc/default/grub add nodmraid to GRUB_CMDLINE_LINUX_DEFAULT:
GRUB_CMDLINE_LINUX_DEFAULT="quiet rhgb nodmraid"
Then re-create the GRUB2 configuration file:
grub2-mkconfig -o /boot/grub2/grub.cfg
Reboot, and no more FakeRAID drive. Success.