dm-stripe
  =========
  
  Device-Mapper's "striped" target is used to create a striped (i.e. RAID-0)
  device across one or more underlying devices. Data is written in "chunks",
  with consecutive chunks rotating among the underlying devices. This can
  potentially provide improved I/O throughput by utilizing several physical
  devices in parallel.
  
  Parameters: <num devs> <chunk size> [<dev path> <offset>]+
      <num devs>: Number of underlying devices.
      <chunk size>: Size of each chunk of data. Must be a power-of-2 and at
                    least as large as the system's PAGE_SIZE.
      <dev path>: Full pathname to the underlying block-device, or a
                  "major:minor" device-number.
      <offset>: Starting sector within the device.
  
  One or more underlying devices can be specified. The striped device size must
  be a multiple of the chunk size and a multiple of the number of underlying
  devices.
  
  
  Example scripts
  ===============
  
  [[
  #!/usr/bin/perl -w
  # Create a striped device across any number of underlying devices. The device
  # will be called "stripe_dev" and have a chunk-size of 128k.
  
  my $chunk_size = 128 * 2;
  my $dev_name = "stripe_dev";
  my $num_devs = @ARGV;
  my @devs = @ARGV;
  my ($min_dev_size, $stripe_dev_size, $i);
  
  if (!$num_devs) {
          die("Specify at least one device
  ");
  }
  
  $min_dev_size = `blockdev --getsize $devs[0]`;
  for ($i = 1; $i < $num_devs; $i++) {
          my $this_size = `blockdev --getsize $devs[$i]`;
          $min_dev_size = ($min_dev_size < $this_size) ?
                          $min_dev_size : $this_size;
  }
  
  $stripe_dev_size = $min_dev_size * $num_devs;
  $stripe_dev_size -= $stripe_dev_size % ($chunk_size * $num_devs);
  
  $table = "0 $stripe_dev_size striped $num_devs $chunk_size";
  for ($i = 0; $i < $num_devs; $i++) {
          $table .= " $devs[$i] 0";
  }
  
  `echo $table | dmsetup create $dev_name`;
  ]]