Very big SSDs
There is a challenge of building SSDs above 128 GB in that the size of an indirection unit (IU) within the NVMe controller has to increase from 4 KiB to something larger in order to be able to address the entire SSD’s capacity within the DRAM budget of the controller. Adding more DRAM into each controller to address larger SSDs at the same IU appears prohibitive because it would require new form factors and significantly increased costs.
Increasing the IU increases the amount of data that the NVMe has to retrieve when a smaller read is issued. For example, a 4K read from an SSD with a 32K IU requires 32K of data to be retrieved from NAND internally. This has power and performance implications that manifest in a less power-efficient SSD for 4K random reads.