dm-stripe — The Linux Kernel 6.14.0-gnu-rt3-parabola1-1-rt documentation

# 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 can potentially provide improved I/O throughput by utilizing several physical devices 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 as large 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 must be 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`;