When running your database through the file system, the read-write lock on each file allows only one active write per file. When you look at the disk statistics using iostat, the disk reports queueing time and service time. The service time is the time that I/O spends on the disk, and the queueing time is how long it waits for all of the other I/Os ahead of it. At the volume level or the file system level, there is no queueing, so vxstatand qiostatdo not show queueing time.

For example, if you send 100 I/Os at the same time and each takes 10 milliseconds, the disk reports an average of 10 milliseconds of service and 490 milliseconds of queueing time. The vxstatand qiostatreport an average of 500 milliseconds service time.