What is the Outstanding Tests in Asynchronous Queue option, "sqlio -o"?

The Outstanding Tests in Asynchronous Queue option, "sqlio -o", specifies the number of I/O tests to be staged in the Outstanding Asynchronous Queue.

The default value is "-o0", no Outstanding I/O tests in the Asynchronous Queue. In this case, all I/O tests are performed synchronously.

Example 1 - Run SQLIO with no tests in the Asynchronous Queue:

C:\fyicenter\SQLIO>sqlio -o0

1 thread reading for 30 secs from file testfile.dat
        using 2KB IOs over 128KB stripes with 64 IOs per run
initialization done
CUMULATIVE DATA:
throughput metrics:
IOs/sec: 12155.57
MBs/sec:    23.74

Example 2 - Run SQLIO with 1 test in the Asynchronous Queue:

C:\fyicenter\SQLIO>sqlio -o1
1 thread reading for 30 secs from file testfile.dat
        using 2KB IOs over 128KB stripes with 64 IOs per run
        enabling multiple I/Os per thread with 1 outstanding
initialization done
CUMULATIVE DATA:
throughput metrics:
IOs/sec: 12417.94
MBs/sec:    24.25

Example 3 - Run SQLIO with 2 tests in the Asynchronous Queue:

C:\fyicenter\SQLIO>sqlio -o2

1 thread reading for 30 secs from file testfile.dat
        using 2KB IOs over 128KB stripes with 64 IOs per run
        enabling multiple I/Os per thread with 2 outstanding
initialization done
CUMULATIVE DATA:
throughput metrics:
IOs/sec: 19060.40
MBs/sec:    37.22

Example 4 - Run SQLIO with 4 test2 in the Asynchronous Queue:

C:\fyicenter\SQLIO>sqlio -o4

1 thread reading for 30 secs from file testfile.dat
        using 2KB IOs over 128KB stripes with 64 IOs per run
        enabling multiple I/Os per thread with 4 outstanding
initialization done
CUMULATIVE DATA:
throughput metrics:
IOs/sec: 20579.95
MBs/sec:    40.19

As you can see, when staging more outstanding tests in the Asynchronous Queue, the throughput is getting better. It seems that the data storage has some capability to perform read operation parallelly with a single thread.

⇒ "sqlio -p" - CPU Number for Affinity

⇐ "sqlio -B" - Hardware/Software Buffering

⇑ Getting Started with Microsoft SQLIO

⇑⇑ SQLIO Disk I/O Benchmark Test Tutorials