1. A method for efficient thresholding of nonvolatile storage (NVS) for a plurality of types of storage rank groups by a processor, comprising: determining each target storage device in a pool of target storage devices as one of a hard disk drive (HDD) and a solid state drive (SSD) device, the each target storage device classified into one of a SSD rank group, a Nearline rank group, an Enterprise rank group, and an Ultra-SSD rank group in the pool of target storage devices, wherein the Nearline rank group and the Enterprise rank group comprise a HDD rank group, and the Nearline rank group, the Enterprise rank group, and the SSD rank group comprise the Non-Ultra-SSD rank group; adjusting thresholds for preventing space allocation in the NVS for at least one of the classified target storage devices based on one of the presence and absence of identified types of the classified target storage devices; setting a threshold of available space in the NVS to allocate at least a majority of available space to one of the HDD rank group, the SSD rank group, and the Ultra-SSD rank group; reducing the threshold of the available space in the NVS to allocate a greater portion of the available space to one of the HDD rank group, the SSD rank group, and the Ultra-SSD rank group; and, identifying when the Ultra-SSD rank group exists with one of the SSD rank group and HDD rank group, the setting of the threshold of the available space in the NVS further comprising: setting the threshold of the available space in the NVS to allocate a maximum of 90 percent of the available space to the Nearline rank group and the Enterprise rank group, which are combined together, when the Ultra-SSD rank group exists and the SSD rank group exists with one of the Enterprise rank group and the Nearline rank group; and setting the threshold of the available space in the NVS to allocate a maximum of 95 percent of the available space to the Nearline rank group, the Enterprise rank group, and the SSD rank group, which are combined together, when the Ultra-SSD rank group exists and the SSD rank group exists with one of the Enterprise rank group and the Nearline rank group, and the adjusting of the thresholds for preventing the space allocation in the NVS further comprising: adjusting the thresholds for preventing the space allocation in the NVS to one of the SSD rank group and the HDD rank group for allocating at least the majority of the available space to the Ultra-SSD rank; and adjusting the thresholds for preventing the space allocation in the NVS to the Ultra-SSD rank group for allocating the majority of the available space to one of the SSD rank group and the HDD rank group.