file rawRead and rawWrite in chunks example

["Nordlöw" via Digitalmars-d-learn]

On Sunday, 9 August 2015 at 10:40:06 UTC, Nordlöw wrote:
> Couldn't the chunk logic be deduced aswell?

Yes :)

See update at:

https://github.com/nordlow/justd/blob/a633b52876388921ec49c189f374746f7b4d8c93/tests/t_rawio.d

> What would a suitable value for `preferred_disk_write_size` be?

Is there a suitable constant somewhere in Phobos?