1. The raidtools package includes the tools you need to set up and maintain a software RAID device (using two or more disk drives in combination for fault tolerance and improved performance) on a Linux system. It only works with Linux 2.2 kernels and later, or with a 2.0 kernel specifically patched with newer RAID support. From Redhat 8.0 RPM

2. Utilities to support 'old-style' RAID disks The Multiple Device driver's main goal is to group several disks or partitions together, making them look like a single block device. This includes linear adding of disks, RAID-0, RAID-4 and -5. If you are creating new RAID arrays, the raidtools2 package and newer RAID drivers may be a better choice. This package may only installed on systems with a kernel version higher than 2.1.62. With kernels from the 2.4 series or newer, or with 2.2 kernels with the 'new-style' RAID-patches, you should use raidtools2 instead. From Debian 3.0r0 APT