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# IO

## Persistent Disk Benchmarking

[Benchmarking persistent disk performance](https://cloud.google.com/compute/docs/disks/benchmarking-pd-performance)

[fio](https://linux.die.net/man/1/fio)

## Buffered I/O vs. Unbuffered I/O

<https://stackoverflow.com/questions/1450551/buffered-vs-unbuffered-io>

* **Buffered I/O:** program structures -> file buffer -> kernel buffer -> disk
  * minimizes system calls
  * minimizes disk I/O
* **Unbuffered I/O:** program structures -> kernel buffer -> disk
  * Used when we want output to be written before continuing (e.g. stderr under C runtime library is usually unbuffered by default, logging library)

**Example**:

* Program reads file 1 byte at a time
* Unbuffered input: goes to disk for every byte (slow)
* Buffered input: Whole block is read into buffer, then individual bytes delivered from buffer area (faster)