I tried to follow well-known formats first, such as WARC and ZIM from Kiwix, so we could benefit from existing tooling support.

For my own custom data format, I have a lot of private code that I plan to release soon. It is optimized for compression, fast lookups, and more. I have been working on it for two years. This is part of a larger, ambitious umbrella project: I am building Google from scratch (all open source), something that anyone can host, including the crawler, indexer, storage, and serving layers. Stay tuned!