Self-contained python script to monitor HDD usage (read/write speed, queue length, and usage percentage)

iomonit.py

import time

# Assuming sector size is 512 bytes
SECTOR_SIZE = 512


def get_disk_stats():
    with open('/sys/block/sda/stat', 'r', encoding='ascii') as f:
        stats = f.readline().split()

        if len(stats) == 11:
            return {
                'read_ios': int(stats[0]),
                'read_merges': int(stats[1]),
                'read_sectors': int(stats[2]),
                'read_ticks': int(stats[3]),
                'write_ios': int(stats[4]),
                'write_merges': int(stats[5]),
                'write_sectors': int(stats[6]),
                'write_ticks': int(stats[7]),
                'in_flight': int(stats[8]),
                'io_ticks': int(stats[9]),
                'time_in_queue': int(stats[10])
            }
        elif len(stats) == 15:
            return {
                'read_ios': int(stats[0]),
                'read_merges': int(stats[1]),
                'read_sectors': int(stats[2]),
                'read_ticks': int(stats[3]),
                'write_ios': int(stats[4]),
                'write_merges': int(stats[5]),
                'write_sectors': int(stats[6]),
                'write_ticks': int(stats[7]),
                'in_flight': int(stats[8]),
                'io_ticks': int(stats[9]),
                'time_in_queue': int(stats[10]),
                'discard_ios': int(stats[11]),
                'discard_merges': int(stats[12]),
                'discard_sectors': int(stats[13]),
                'discard_ticks': int(stats[14])
            }
        elif len(stats) == 17:
            return {
                'read_ios': int(stats[0]),
                'read_merges': int(stats[1]),
                'read_sectors': int(stats[2]),
                'read_ticks': int(stats[3]),
                'write_ios': int(stats[4]),
                'write_merges': int(stats[5]),
                'write_sectors': int(stats[6]),
                'write_ticks': int(stats[7]),
                'in_flight': int(stats[8]),
                'io_ticks': int(stats[9]),
                'time_in_queue': int(stats[10]),
                'discard_ios': int(stats[11]),
                'discard_merges': int(stats[12]),
                'discard_sectors': int(stats[13]),
                'discard_ticks': int(stats[14]),
                'flush_ios': int(stats[15]),
                'flush_ticks': int(stats[16])
            }
        else:
            raise ValueError("Unexpected number of fields in /sys/block/sda/stat: {}".format(len(stats)))


if __name__ == "__main__":
    prev_stats = get_disk_stats()
    prev_time = time.time()
    while True:
        time.sleep(1)
        curr_stats = get_disk_stats()
        curr_time = time.time()
        interval = curr_time - prev_time

        write_speed = (curr_stats['write_sectors'] - prev_stats['write_sectors']) * SECTOR_SIZE / interval
        time_busy_percent = (curr_stats['io_ticks'] - prev_stats['io_ticks']) / (interval * 10)

        read_speed = (curr_stats['read_sectors'] - prev_stats['read_sectors']) * SECTOR_SIZE / interval
        avg_queue_size = (curr_stats['time_in_queue'] - prev_stats['time_in_queue']) / interval / 1000

        read_iops = (curr_stats['read_ios'] - prev_stats['read_ios']) / interval
        write_iops = (curr_stats['write_ios'] - prev_stats['write_ios']) / interval

        print("Read: {:8.2f} MB/s - {:7.2f} IOPS - Write: {:8.2f} MB/s - {:7.2f} IOPS - Busy: {:7.2f} % - Queue: {:5.2f}".format(
            read_speed / 1000,
            read_iops,
            write_speed / 1000,
            write_iops,
            time_busy_percent,
            avg_queue_size))

        prev_stats = curr_stats
        prev_time = curr_time