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 canpotentially provide improved I/O throughput by utilizing several physicaldevices 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 at least aslarge 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 mustbe a multiple of the chunk size multiplied by 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\n");}$min_dev_size = `blockdev --getsz $devs[0]`;for ($i = 1; $i < $num_devs; $i++) {        my $this_size = `blockdev --getsz $devs[$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`;