cassandra read high iowait

Question

data read per second

I have a three node cassandra cluster。when I have multi thread querying from the cluster ,the io load is very high.The cluster holds about 80GB data per node.I use time window compact strategy and time-window is ten hour.One sstable is about 1GB.Can some body help me with it.Thank you.one sstable infomation
data is at a speed of 10000 per second .the cluster holds about 10 billion records . below is the schema information

CREATE TABLE point_warehouse.point_period (
    point_name text,
    year text,
    time timestamp,
    period int,
    time_end timestamp,
    value text,
    PRIMARY KEY ((point_name, year), time)
) WITH CLUSTERING ORDER BY (time DESC)
    AND bloom_filter_fp_chance = 0.01
    AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
    AND comment = ''
    AND compaction = {'class': 'org.apache.cassandra.db.compaction.TimeWindowCompactionStrategy', 'compaction_window_size': '10', 'compaction_window_unit': 'HOURS', 'max_threshold': '32', 'min_threshold': '4'}
    AND compression = {'chunk_length_in_kb': '64', 'class': 'org.apache.cassandra.io.compress.LZ4Compressor'}
    AND crc_check_chance = 1.0
    AND dclocal_read_repair_chance = 0.1
    AND default_time_to_live = 2592000
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND read_repair_chance = 0.0
    AND speculative_retry = '99PERCENTILE';

and the query is SELECT * from POINT_PERIOD where POINT_NAME=? AND YEAR='2017' AND TIME >'2017-05-23 12:53:24 order by time asc LIMIT 1 ALLOW FILTERING'

when execute this query concurrently the io load became extremely high like 200MB/s. thank you .