Ask HN: What are some good resources for learning about low level disk/file IO?

I've been messing around with writing a toy database for fun/learning, and realised I've got a fairly big gap in my knowledge when it comes to dealing with performance and durability when dealing with file reads/writes.

Example of some questions I'd like to be able to answer or at least make reasonable decisions about (note: I don't actually want any answers to the above now, they're just examples of the sort of thing I'd like to read in depth about, and build up some background knowledge):

  * how to ensure data's been safely written (e.g. when to flush, fsync, what
    guarantees that gives, using WAL)
  * blocks sizes to read/write for different purposes, tradeoffs, etc.
  * considerations for writing to different media/filesystems (e.g. disk, ssd, NFS)
  * when to rely on OS disk cache vs. using own cache
  * when to use/not use mmap
  * performance considerations (e.g. multiple small files vs. few larger ones,
    concurrent readers/writers, locking, etc.)
  * OS specific considerations

I recall reading some posts (related to Redis/SQLite/Postgres) related to this, which made me realise that it's a fairly complex topic, but not one I've found a good entry point for.

Any pointers to books, documentation, etc. on the above would be much appreciated.