1 =========
2 dm-stripe
3 =========
4
5 Device-Mapper's "striped" target is used to create a striped (i.e. RAID-0)
6 device across one or more underlying devices. Data is written in "chunks",
7 with consecutive chunks rotating among the underlying devices. This can
8 potentially provide improved I/O throughput by utilizing several physical
9 devices in parallel.
10
11 Parameters: <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
23 One or more underlying devices can be specified. The striped device size must
24 be a multiple of the chunk size multiplied by the number of underlying devices.
25
26
27 Example 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`;
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.