Created
October 16, 2018 16:06
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dd optimal blocksize detection
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#!/bin/bash | |
# | |
# Copied from: https://github.com/tdg5/blog/blob/master/_includes/scripts/dd_obs_test.sh | |
# | |
# Since we're dealing with dd, abort if any errors occur | |
set -e | |
TEST_FILE=${1:-dd_obs_testfile} | |
TEST_FILE_EXISTS=0 | |
if [ -e "$TEST_FILE" ]; then TEST_FILE_EXISTS=1; fi | |
TEST_FILE_SIZE=134217728 | |
if [ $EUID -ne 0 ]; then | |
echo "NOTE: Kernel cache will not be cleared between tests without sudo. This will likely cause inaccurate results." 1>&2 | |
fi | |
# Header | |
PRINTF_FORMAT="%8s : %s\n" | |
printf "$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 | |
# Clear kernel cache to ensure more accurate test | |
[ $EUID -eq 0 ] && [ -e /proc/sys/vm/drop_caches ] && echo 3 > /proc/sys/vm/drop_caches | |
# Create a test file with the specified block size | |
DD_RESULT=$(dd if=/dev/zero of=$TEST_FILE bs=$BLOCK_SIZE count=$COUNT conv=fsync 2>&1 1>/dev/null) | |
# Extract the transfer rate from dd's STDERR output | |
TRANSFER_RATE=$(echo $DD_RESULT | \grep --only-matching -E '[0-9.]+ ([MGk]?B|bytes)/s(ec)?') | |
# Clean up the test file if we created one | |
if [ $TEST_FILE_EXISTS -ne 0 ]; then rm $TEST_FILE; fi | |
# Output the result | |
printf "$PRINTF_FORMAT" "$BLOCK_SIZE" "$TRANSFER_RATE" | |
done |
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