Storage shouldn't be counted in SI units in the first place. Throughput is arguably semi-legitimate to count in SI, but for storage? There is literally no reason other than marketing.
It makes no sense to count it in 1000-based SI units. You'll perpetually mis-align the data in whichever underlying storage technology you're using, and it's bad for performance and resource consumption.
Ask for disk sector alignment; we don’t have disk sectors any more, we use SSDs with blocks. And the sizes don’t need to have a neat number of kilobytes. Just the same as a litre of water doesn’t have a neat number of H2O molecules in it.