Comment by raggi

SQLite has an online backup API as well, but it is slower and requires a significant additional page cache cost.

The team chose SQLite early on (there are some blog posts about this) and then we vertically scaled against the SQLite architecture. There are subtle ways you come to depend on the proximity/latency when you scale with local storage that mean switching requires a lot of non-obvious work - it’s probably the largest hazard for embracing SQLite in a growing saas - but at the same time you can push the vertical scale pretty far, which has great margins.

Had we scaled a different architecture of database there’s little reason to believe it would have been plain sailing as seems to be implied here.