How do you optimize the disk IO when you cannot assume a file will start at a boundary then?

Hi All,

I understand the storage layer in databases goes to great lengths to ensure:
- a row does not cross a block boundary
- read/writes/allocation happen in units of blocks
etc. The motivation is that at the OS level, it reads and writes pages
(blocks), not individual bytes. I am only concerned about SSDs but I think
the principle applies to HDD as well.

but how can we do all this when we are not even guaranteed that the
beginning of a file will be aligned with a block boundary? refer this
<https://stackoverflow.com/questions/8018449/is-it-guaranteed-that-the-beginning-of-a-file-is-aligned-with-pagesize-of-file-s>
.

Further, I don't see any APIs exposing I/O operations in terms of blocks.
All File I/O APIs I see expose a file as a randomly accessible contiguous
byte buffer. Would it not have been easier if there were APIs that exposed
I/O operations in terms of blocks?

can someone explain this to me?

Sid