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.
The 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 zero, the storage subsystem is not used. If the value is a non-zero number, sustained over time, then constant interaction with the storage subsystem takes place.
The 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 waiting to be managed by the kernel when the driver's active command buffer is full. Occasionally, a queue will...