In the ongoing discussion about the future of Bcachefs in the mainline Linux kernel, someone mentioned an interesting anecdote about Btrfs. Meta (Facebook) has long been one of the most prominent users of the Btrfs file system. Meta employs many engineers working on the Btrfs file system and has been known for using the system in production environments for many years.
This is nothing new, there have been similar demonstrations in the past, such as how Meta relies on Btrfs to build its "entire infrastructure":
Meta's well-known Btrfs engineer Josef Bacik wrote about the extent of the impact on Meta's use of Btrfs:
Meta infrastructure is built entirely on btrfs and its functionality. With the power and robustness of btrfs, we've saved billions of dollars in infrastructure costs.
Given the scale of Meta's operations and its massive infrastructure, Btrfs is credited with saving "billions of dollars" due to its advanced feature set and robustness. This is an interesting story for those who still question Btrfs or its suitability for use in production environments.
You can find more comments via this LKML thread in the ongoing discussion about Bcachefs in the mainline Linux kernel.