I'm speculating here based on my experience working on a storage fabric product in the past. First - it's sensible to have limits to the size of the block list

I'm speculating here based on my experience working on a storage fabric product in the past. First - it's sensible to have limits to the size of the block list. These systems usually have a metadata layer and a block layer. In order to ensure a latency SLO, some reasonable limits to the number of blocks need to be imposed. This also prevents creating files with many blocks of small sizes. More below. Second - Usually blocks are designed to match some physical characteristics of the storage device, but 10 MB doesn't match anything. 8MB might be a block size for an SSD or a HDD, or 72MB=9*8MB might be a block size with 9:16 erasure coding, which they likely have for backup use-cases. That being said, it's likely the block size is not fixed to 10 MB and could be increased (or decreased). Whether or not the client program that does the upload is aware of that, is a different problem.