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Bytes/Transfer=Bytes/Read + Bytes/Write

  • May 13, 2006 at 7:14 am

    #152970

    Hi All

    I have scheduled the below counters.

    Physical Disk\Avg. Disk Bytes/Tranfer

    Physical Disk\Avg. Disk Bytes/Read

    Physical Disk\Avg. Disk Bytes/Write

    Since one Tranfer operation includes both Read and Write Operations. By adding the values from the counters of both Read and Write opertions at a particular time, I should get the Bytes/Transfer value at that time. But why is that iam not getting.

    Any thoughts?

  • May 16, 2006 at 4:44 am

    #638097

    Ashwin

    The way I interpret it is that a Transfer is a Read or a Write.  To quote from the explanation given in the Performance application, "Avg. Disk Bytes/Transfer is the average number of bytes transferred to or from the disk during write or read operations." Also, "Avg. Disk Bytes/Read is the average number of bytes transferred from the disk during read operations."

    From the above, you might conclude that the Avg. Disk Bytes/Transfer would be an average of Avg. Disk Bytes/Read and Avg. Disk Bytes/Write.  However, that would only be right if the number of reads were the same as the number of writes.

    For example, suppose you have 100 reads of 1000 bytes each and 50 reads of 500 bytes each.  Then the average bytes per read is 100 and average bytes per write is 50.  However, the average bytes per transfer is not going to be 750 (or 1500), but (100 * 1000 + 50 * 500) / (100 + 50) = 833.3333.

    Does that make sense?

    John

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