Filesystem Internals

Understanding why files are three separate layers, not one.

Skipping a costly data copy by pointing directly at kernel memory makes mmap blazingly fast.

Append-only logs let databases promise speed and safety without compromising either.

Working set size determines whether your reads and writes hit memory speed or disk speed.

Linux offers two incompatible locking mechanisms that don't see each other on local filesystems.

Atomicity at the filesystem level doesn't guarantee data survives crashes.

Understanding POSIX's three non-negotiable guarantees keeps your code from silently corrupting data.