Monitoring command queuing
There are metrics for monitoring the number of active disk commands and the number of disk commands that are queued. These metrics provide information about your disk performance. They are often used to further interpret the latency values that you might be observing.
Number of active commands: This metric represents the number of I/O operations that are currently active. This includes operations for which the host is processing. This metric can serve as a quick view of storage activity. If the value of this metric is close to or at zero, the storage subsystem is not being used. If the value is a nonzero number, sustained over time, then constant interaction with the storage subsystem is occurring.
Number of commands queued: This metric represents the number of I/O operations that require processing but have not yet been addressed. Commands are queued and awaiting management by the kernel when the driver's active command buffer is full. Occasionally, a queue will...
