How to verify disk hit by a query

I want to know how to verify disk hits by a select query in PostgreSQL 9.4 on CentOS 6.5. Also please let me know how far enabling the log_statement_stats in the postgresql.conf will help me.

I need to understand the ‘filesystem blocks in/out’ value in the logs when I switch the above parameter to on.

For example, please check the log snippet:

2016-02-03 14:12:45 PST LOG:  statement: select * from test_stats_collect ;
2016-02-03 14:12:45 PST LOG:  QUERY STATISTICS
2016-02-03 14:12:45 PST DETAIL:  ! system usage stats:
        !       0.069489 elapsed 0.027995 user 0.002999 system sec
        !       [0.131979 user 0.146977 sys total]
        !       0/0 [3280/26440] filesystem blocks in/out
        !       0/5 [19/4866] page faults/reclaims, 0 [0] swaps
        !       0 [0] signals rcvd, 0/0 [0/0] messages rcvd/sent
        !       20/116 [125/174] voluntary/involuntary context switches