How to check IO performance? (Oracle)

During performance tuning or being called to debug a performance issues of the database system, we always would like to know the current I/O status and how it compares with baseline periods. This is a handy script that would give you useful information.

Please keep in mind that busy I/O might not necessary lead to the conclusion that I/O is the bottleneck or culprit of the performance issue.

prompt ====================================================
prompt == Start of check_io.sql
prompt ====================================================

prompt ====================================================
prompt == Check IO notes
prompt == OS level should support Async for better performance.
prompt == In general, for waits 1000+ per hour, elapsed time
prompt == should be less than 15~20ms.
prompt ==
prompt == Single Block -->wait on db file sequential read -->index visit or rollback
prompt ==
prompt == Multi Block -->wait on db file scattered read -->full table scan or index fast full scan
prompt ==
prompt ==
prompt ==
prompt == How to Tell if the I/O of the Database is Slow (Doc ID 1275596.1)
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prompt ====================================================
prompt == Show IO Stats
prompt ====================================================
set lines 300
set pages 300
select * from DBA_HIST_IOSTAT_DETAIL;

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prompt == Show IO Metric
prompt ====================================================
select * from dba_hist_sysmetric_history where metric_name like 'I/O%Megabytes%';

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prompt == End of check_io.sql
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