Mdadm is the modern tool most Linux distributions use these days to manage software RAID arrays; in the past raidtools was the tool we have used for th

mdadm [mode] [options]

RAID devices are virtual devices created from two or more real block
devices. This allows multiple devices (typically disk drives or parti-
tions there-of) to be combined into a single device to hold (for exam-
ple) a single filesystem. Some RAID levels include redundancy and so
can survive some degree of device failure.

Linux Software RAID devices are implemented through the md (Multiple
Devices) device driver.

Currently, Linux supports LINEAR md devices, RAID0 (striping), RAID1
(mirroring), RAID4, RAID5, RAID6, MULTIPATH, and FAULTY.

MULTIPATH is not a Software RAID mechanism, but does involve multiple
devices. For MULTIPATH each device is a path to one common physical
storage device.

FAULTY is also no true RAID, and it only involves one device. It pro-
vides a layer over a true device that can be used to inject faults.

mdadm is a program that can be used to create, manage, and monitor MD
devices. As such it provides a similar set of functionality to the
raidtools packages. The key differences between mdadm and raidtools

· mdadm is a single program and not a collection of programs.

· mdadm can perform (almost) all of its functions without having a
configuration file and does not use one by default. Also mdadm
helps with management of the configuration file.

· mdadm can provide information about your arrays (through Query,
Detail, and Examine) that raidtools cannot.