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Support non-power-of-2 chunk sizes with dm striping for proper alignment of stripe IO on storage that has non-power-of-2 optimal IO sizes (e.g. RAID6 10+2). Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
58 lines
1.8 KiB
Plaintext
58 lines
1.8 KiB
Plaintext
dm-stripe
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=========
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Device-Mapper's "striped" target is used to create a striped (i.e. RAID-0)
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device across one or more underlying devices. Data is written in "chunks",
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with consecutive chunks rotating among the underlying devices. This can
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potentially provide improved I/O throughput by utilizing several physical
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devices in parallel.
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Parameters: <num devs> <chunk size> [<dev path> <offset>]+
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<num devs>: Number of underlying devices.
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<chunk size>: Size of each chunk of data. Must be at least as
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large as the system's PAGE_SIZE.
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<dev path>: Full pathname to the underlying block-device, or a
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"major:minor" device-number.
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<offset>: Starting sector within the device.
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One or more underlying devices can be specified. The striped device size must
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be a multiple of the chunk size multiplied by the number of underlying devices.
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Example scripts
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===============
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[[
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#!/usr/bin/perl -w
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# Create a striped device across any number of underlying devices. The device
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# will be called "stripe_dev" and have a chunk-size of 128k.
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my $chunk_size = 128 * 2;
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my $dev_name = "stripe_dev";
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my $num_devs = @ARGV;
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my @devs = @ARGV;
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my ($min_dev_size, $stripe_dev_size, $i);
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if (!$num_devs) {
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die("Specify at least one device\n");
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}
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$min_dev_size = `blockdev --getsize $devs[0]`;
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for ($i = 1; $i < $num_devs; $i++) {
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my $this_size = `blockdev --getsize $devs[$i]`;
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$min_dev_size = ($min_dev_size < $this_size) ?
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$min_dev_size : $this_size;
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}
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$stripe_dev_size = $min_dev_size * $num_devs;
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$stripe_dev_size -= $stripe_dev_size % ($chunk_size * $num_devs);
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$table = "0 $stripe_dev_size striped $num_devs $chunk_size";
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for ($i = 0; $i < $num_devs; $i++) {
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$table .= " $devs[$i] 0";
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}
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`echo $table | dmsetup create $dev_name`;
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]]
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