Examples include selectively adjusting I/O Q-connections between an NVMe controller and a storage device in an NVMe system. In some examples, a utilization time of a host port in an NVMe controller is determined. In response to determining that the utilization time of the host port is lower than a host port utilization threshold and a number of I/O Q-connections at the storage device is less than an I/O Q-connection threshold for the storage device, a candidate list of storage devices is created, each storage devices included in the candidate list having an average service time greater than or equal to an average service time of a host port associated with the storage device. For each storage device included in the candidate list, processing time and I/O block size of I/O requests at the storage device is determined and a number of I/O Q-connections at the storage device is selectively adjusted based on the processing time and I/O block size of I/O requests at the storage device.