AWR IO throughput discrepancies

Question

The following is the IOStat by Function summary section of an awr report:
IOStat by Function summary          DB/Inst: FIZ6486/fiz6486  Snaps: 3724-3725
-> 'Data' columns suffixed with M,G,T,P are in multiples of 1024
    other columns suffixed with K,M,G,T,P are in multiples of 1000
-> ordered by (Data Read + Write) desc
                Reads:   Reqs   Data    Writes:  Reqs   Data    Waits:    Avg
Function Name   Data    per sec per sec Data    per sec per sec Count    Tm(ms)
LGWR                 1M     0.0 .001151   27.6G    37.3 32.5505    6284   180.3
DBWR                 0M     0.0      0M   15.5G   190.4 18.2959  161.1K     4.9
Others              32M     2.6 .036833     24M     1.8 .027625    3368     3.2
Buffer Cache Re      8M     1.1 .009208      0M     0.0      0M     977    19.2
Direct Reads         1M     0.1 .001151      0M     0.0      0M      54     0.8
Direct Writes        0M     0.0      0M      0M     0.0      0M      42     1.3
Streams AQ           0M     0.0      0M      0M     0.0      0M       6    78.2
TOTAL:              42M     3.8 .048344   43.2G   229.6 50.8741  171.8K    11.3
          -------------------------------------------------------------The period between the snapshots (for which the report was generated) was about 597 seconds. The throughput then should be at least 43.2G/597 seconds = 72.36 MB/s, which is considerably higher than the reported throughput of 50.87 MB/s.
Is there any document that can help me understand the seeming discrepancies?

Answer 1

user599896 wrote:
The following is the IOStat by Function summary section of an awr report:
Reads:   Reqs   Data    Writes:  Reqs   Data    Waits:    Avg
Function Name   Data    per sec per sec Data    per sec per sec Count    Tm(ms)
TOTAL:              42M     3.8 .048344   43.2G   229.6 50.8741  171.8K    11.3
-------------------------------------------------------------The period between the snapshots (for which the report was generated) was about 597 seconds. The throughput then should be at least 43.2G/597 seconds = 72.36 MB/s, which is considerably higher than the reported throughput of 50.87 MB/s.
My first guess would be that you've got a fifteen minute snapshot rather than a 10 minute snapshot, so Oracle is dividing by roughly 900 rather than roughly 600. Can you post the snapshot summary detail (start/stop time).
Regards
Jonathan Lewis