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f0ba4377 MCC |
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`; |