ARCHIL

A field guide

How file systems work

How files are named, written, cached, shared, copied, and billed, from the kernel to the cloud, taught one step at a time with figures you can drive.

Hunter LeathFounder & CEO, Archil

Checked November 2026The whole guide as Markdown

Contents

  1. 01From a path to an inodeHow a POSIX file system names, finds, and changes a file, from inodes and directories through path lookup, descriptors, rename, links, and permission bits. Then how an object store’s keys map onto that model, and the four places where they can’t.
  2. 02Where fsync returns fromHow one write travels from a program’s memory to a drive’s flash and then to other machines, what write(), fsync(), fdatasync(), and O_DIRECT each wait for, and why replicated storage acknowledges where it does. By the end, you can name the layer any storage system acknowledges from, and the failures that choice survives.
  3. 03Anatomy of a file create over a networkWhat a program asks for when it creates one small file, why a network file system has to ask a server before it can answer, and how callbacks, leases, and delegations let a client answer from its own memory once it holds the right to.
  4. 04One file, many cachesWhat a second machine sees after you write a file, and who gets to write it next. By the end you can tell linearizable, close-to-open, and eventual consistency apart, explain how a cache learns it’s stale, and say why leases exist and why locks across machines are harder than they look.
  5. 05A file system on an object storeHow a tree of files, with its modes, links, and renames, gets laid onto a flat map of immutable objects. By the end, you can read any product’s bucket layout and say what it gives up, what it costs to rename and list, and what happens when someone else writes to the bucket.
  6. 06Copy-on-write, block by blockHow a file system can copy a terabyte by writing one block, why the same design survives a power cut, and why deleting a snapshot takes more work than taking one. By the end you’ll be able to explain snapshots, clones, and their space accounting from the blocks up.
  7. 07How storage is meteredWhy a provider sells storage as reserved capacity or as bytes stored, what a GB-month measures, why cold data costs less to keep and more to read, and why, for agents, an idle machine costs more than the bytes it holds.