1=========
2dm-stripe
3=========
4
5Device-Mapper's "striped" target is used to create a striped (i.e. RAID-0)
6device across one or more underlying devices. Data is written in "chunks",
7with consecutive chunks rotating among the underlying devices. This can
8potentially provide improved I/O throughput by utilizing several physical
9devices in parallel.
10
11Parameters: <num devs> <chunk size> [<dev path> <offset>]+
12    <num devs>:
13	Number of underlying devices.
14    <chunk size>:
15	Size of each chunk of data. Must be at least as
16        large as the system's PAGE_SIZE.
17    <dev path>:
18	Full pathname to the underlying block-device, or a
19	"major:minor" device-number.
20    <offset>:
21	Starting sector within the device.
22
23One or more underlying devices can be specified. The striped device size must
24be a multiple of the chunk size multiplied by the number of underlying devices.
25
26
27Example scripts
28===============
29
30::
31
32  #!/usr/bin/perl -w
33  # Create a striped device across any number of underlying devices. The device
34  # will be called "stripe_dev" and have a chunk-size of 128k.
35
36  my $chunk_size = 128 * 2;
37  my $dev_name = "stripe_dev";
38  my $num_devs = @ARGV;
39  my @devs = @ARGV;
40  my ($min_dev_size, $stripe_dev_size, $i);
41
42  if (!$num_devs) {
43          die("Specify at least one device\n");
44  }
45
46  $min_dev_size = `blockdev --getsz $devs[0]`;
47  for ($i = 1; $i < $num_devs; $i++) {
48          my $this_size = `blockdev --getsz $devs[$i]`;
49          $min_dev_size = ($min_dev_size < $this_size) ?
50                          $min_dev_size : $this_size;
51  }
52
53  $stripe_dev_size = $min_dev_size * $num_devs;
54  $stripe_dev_size -= $stripe_dev_size % ($chunk_size * $num_devs);
55
56  $table = "0 $stripe_dev_size striped $num_devs $chunk_size";
57  for ($i = 0; $i < $num_devs; $i++) {
58          $table .= " $devs[$i] 0";
59  }
60
61  `echo $table | dmsetup create $dev_name`;
62