drivers/md/Config.help

CONFIG_BLK_DEV_LVM
  This driver lets you combine several hard disks, hard disk
  partitions, multiple devices or even loop devices (for evaluation
  purposes) into a volume group.  Imagine a volume group as a kind of
  virtual disk. Logical volumes, which can be thought of as virtual
  partitions, can be created in the volume group.  You can resize
  volume groups and logical volumes after creation time, corresponding
  to new capacity needs.  Logical volumes are accessed as block
  devices named /dev/VolumeGroupName/LogicalVolumeName.

  For details see <file:Documentation/LVM-HOWTO>.  You will need
  supporting user space software; location is in
  <file:Documentation/Changes>.

  If you want to compile this support as a module ( = code which can
  be inserted in and removed from the running kernel whenever you
  want), say M here and read <file:Documentation/modules.txt>.  The
  module will be called lvm-mod.o.

CONFIG_MD
  Support multiple physical spindles through a single logical device.
  Required for RAID and logical volume management (LVM).

CONFIG_BLK_DEV_MD
  This driver lets you combine several hard disk partitions into one
  logical block device. This can be used to simply append one
  partition to another one or to combine several redundant hard disks
  into a RAID1/4/5 device so as to provide protection against hard
  disk failures. This is called "Software RAID" since the combining of
  the partitions is done by the kernel. "Hardware RAID" means that the
  combining is done by a dedicated controller; if you have such a
  controller, you do not need to say Y here.

  More information about Software RAID on Linux is contained in the
  Software RAID mini-HOWTO, available from
  <http://www.linuxdoc.org/docs.html#howto>. There you will also learn
  where to get the supporting user space utilities raidtools.

  If unsure, say N.

CONFIG_MD_LINEAR
  If you say Y here, then your multiple devices driver will be able to
  use the so-called linear mode, i.e. it will combine the hard disk
  partitions by simply appending one to the other.

  If you want to compile this as a module ( = code which can be
  inserted in and removed from the running kernel whenever you want),
  say M here and read <file:Documentation/modules.txt>.  The module
  will be called linear.o.

  If unsure, say Y.

CONFIG_MD_RAID0
  If you say Y here, then your multiple devices driver will be able to
  use the so-called raid0 mode, i.e. it will combine the hard disk
  partitions into one logical device in such a fashion as to fill them
  up evenly, one chunk here and one chunk there. This will increase
  the throughput rate if the partitions reside on distinct disks.

  Information about Software RAID on Linux is contained in the
  Software-RAID mini-HOWTO, available from
  <http://www.linuxdoc.org/docs.html#howto>. There you will also
  learn where to get the supporting user space utilities raidtools.

  If you want to compile this as a module ( = code which can be
  inserted in and removed from the running kernel whenever you want),
  say M here and read <file:Documentation/modules.txt>.  The module
  will be called raid0.o.

  If unsure, say Y.

CONFIG_MD_RAID1
  A RAID-1 set consists of several disk drives which are exact copies
  of each other.  In the event of a mirror failure, the RAID driver
  will continue to use the operational mirrors in the set, providing
  an error free MD (multiple device) to the higher levels of the
  kernel.  In a set with N drives, the available space is the capacity
  of a single drive, and the set protects against a failure of (N - 1)
  drives.

  Information about Software RAID on Linux is contained in the
  Software-RAID mini-HOWTO, available from
  <http://www.linuxdoc.org/docs.html#howto>.  There you will also
  learn where to get the supporting user space utilities raidtools.

  If you want to use such a RAID-1 set, say Y. This code is also
  available as a module called raid1.o ( = code which can be inserted
  in and removed from the running kernel whenever you want).  If you
  want to compile it as a module, say M here and read
  <file:Documentation/modules.txt>.

  If unsure, say Y.

CONFIG_MD_RAID5
  A RAID-5 set of N drives with a capacity of C MB per drive provides
  the capacity of C * (N - 1) MB, and protects against a failure
  of a single drive. For a given sector (row) number, (N - 1) drives
  contain data sectors, and one drive contains the parity protection.
  For a RAID-4 set, the parity blocks are present on a single drive,
  while a RAID-5 set distributes the parity across the drives in one
  of the available parity distribution methods.

  Information about Software RAID on Linux is contained in the
  Software-RAID mini-HOWTO, available from
  <http://www.linuxdoc.org/docs.html#howto>. There you will also
  learn where to get the supporting user space utilities raidtools.

  If you want to use such a RAID-4/RAID-5 set, say Y. This code is
  also available as a module called raid5.o ( = code which can be
  inserted in and removed from the running kernel whenever you want).
  If you want to compile it as a module, say M here and read
  <file:Documentation/modules.txt>.

  If unsure, say Y.

CONFIG_MD_MULTIPATH
  Multipath-IO is the ability of certain devices to address the same
  physical disk over multiple 'IO paths'. The code ensures that such
  paths can be defined and handled at runtime, and ensures that a
  transparent failover to the backup path(s) happens if a IO errors
  arrives on the primary path.

  If unsure, say N.