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1da177e4 LT |
1 | dm-stripe |
2 | ========= | |
3 | ||
4 | Device-Mapper's "striped" target is used to create a striped (i.e. RAID-0) | |
5 | device across one or more underlying devices. Data is written in "chunks", | |
6 | with consecutive chunks rotating among the underlying devices. This can | |
7 | potentially provide improved I/O throughput by utilizing several physical | |
8 | devices in parallel. | |
9 | ||
10 | Parameters: <num devs> <chunk size> [<dev path> <offset>]+ | |
11 | <num devs>: Number of underlying devices. | |
eb850de6 MS |
12 | <chunk size>: Size of each chunk of data. Must be at least as |
13 | large as the system's PAGE_SIZE. | |
1da177e4 LT |
14 | <dev path>: Full pathname to the underlying block-device, or a |
15 | "major:minor" device-number. | |
16 | <offset>: Starting sector within the device. | |
17 | ||
18 | One or more underlying devices can be specified. The striped device size must | |
f14fa693 | 19 | be a multiple of the chunk size multiplied by the number of underlying devices. |
1da177e4 LT |
20 | |
21 | ||
22 | Example scripts | |
23 | =============== | |
24 | ||
25 | [[ | |
26 | #!/usr/bin/perl -w | |
27 | # Create a striped device across any number of underlying devices. The device | |
28 | # will be called "stripe_dev" and have a chunk-size of 128k. | |
29 | ||
30 | my $chunk_size = 128 * 2; | |
31 | my $dev_name = "stripe_dev"; | |
32 | my $num_devs = @ARGV; | |
33 | my @devs = @ARGV; | |
34 | my ($min_dev_size, $stripe_dev_size, $i); | |
35 | ||
36 | if (!$num_devs) { | |
37 | die("Specify at least one device\n"); | |
38 | } | |
39 | ||
40 | $min_dev_size = `blockdev --getsize $devs[0]`; | |
41 | for ($i = 1; $i < $num_devs; $i++) { | |
42 | my $this_size = `blockdev --getsize $devs[$i]`; | |
43 | $min_dev_size = ($min_dev_size < $this_size) ? | |
44 | $min_dev_size : $this_size; | |
45 | } | |
46 | ||
47 | $stripe_dev_size = $min_dev_size * $num_devs; | |
48 | $stripe_dev_size -= $stripe_dev_size % ($chunk_size * $num_devs); | |
49 | ||
50 | $table = "0 $stripe_dev_size striped $num_devs $chunk_size"; | |
51 | for ($i = 0; $i < $num_devs; $i++) { | |
52 | $table .= " $devs[$i] 0"; | |
53 | } | |
54 | ||
55 | `echo $table | dmsetup create $dev_name`; | |
56 | ]] | |
57 |