dd of=file if=/dev/zero bs=512 count=1000000
dd of=file if=/dev/zero bs=512 count=1000000 oflag=direct

sync; echo 3 > /proc/sys/vm/drop_caches

cd /usr/local/bin
curl -O https://raw.githubusercontent.com/cxcv/iops/master/iops
chmod a+rx iops

iops /dev/sdb

iops /dev/sda

dd if=file of=/dev/null

dd if=file iflag=direct of=/dev/null

dd if=/dev/sda of=/dev/null

dd if=/dev/sdb

dd if=/dev/sdb of=/dev/null

iostat -xmt 1 /dev/sda

cat /sys/block/sdb/queue/max_sectors_kb

echo "1024" > /sys/block/sdb/queue/max_sectors_kb

blktrace -d /dev/sda -o - | blkparse -i -