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--- check_for_optimal_dd_blocksize [2018/07/05 08:50] – created admin
+++ check_for_optimal_dd_blocksize [2018/07/05 08:50] (current) – admin
@@ Line 1: / Line 1: @@
+<code>
+#!/bin/bash
+# Since we're dealing with dd, abort if any errors occur
+set -e
+TEST_FILE=${1:-dd_obs_testfile}
+[ -e "$TEST_FILE" ]; TEST_FILE_EXISTS=$?
+TEST_FILE_SIZE=134217728
+# Header
+PRINTF_FORMAT="%8s : %s\n"
+printf "$PRINTF_FORMAT" 'block size' 'transfer rate'
+# Block sizes of 512b 1K 2K 4K 8K 16K 32K 64K 128K 256K 512K 1M 2M 4M 8M 16M 32M 64M
+for BLOCK_SIZE in 512 1024 2048 4096 8192 16384 32768 65536 131072 262144 524288 1048576 2097152 4194304 8388608 16777216 33554432 67108864
+do
+  # Calculate number of segments required to copy
+  COUNT=$(($TEST_FILE_SIZE / $BLOCK_SIZE))
+  if [ $COUNT -le 0 ]; then
+    echo "Block size of $BLOCK_SIZE estimated to require $COUNT blocks, aborting further tests."
+    break
+  fi
+  # Create a test file with the specified block size
+  DD_RESULT=$(dd if=/dev/zero of=$TEST_FILE bs=$BLOCK_SIZE count=$COUNT 2>&1 1>/dev/null)
+  # Extract the transfer rate from dd's STDERR output
+  TRANSFER_RATE=$(echo $DD_RESULT | \grep --only-matching -E '[0-9.]+ ([MGk]?B|bytes)/s(ec)?')
+  # Clean up the test file if we created one
+  [ $TEST_FILE_EXISTS -ne 0 ] && rm $TEST_FILE
+  # Output the result
+  printf "$PRINTF_FORMAT" "$BLOCK_SIZE" "$TRANSFER_RATE"
+done
+</code>
 credits go to: [[http://blog.tdg5.com/tuning-dd-block-size/]]