Compared to btrfs it's claimed to be faster and having working RAID support.
Its unique feature is using a fast device as cache to speed up access to slower, larger disks, I think.
Yes. The intelligent multi-device-type feature is a huge improvement for any workload that needs more space than what an SSD can affordably provide, even moreso with the reliability of eg RAID1.
Before that I had to use BTRFS (RAID1) on bcache (not fs) devices, but half of the cache space was being wasted on the redundant copies because the two systems operate independently.
Compared to ZFS, it's a sideways movement except for being in the kernel. ZFS has a lot more enterprise level features and an excellent track record. Its used widely for some pretty big installations, and still can be used by the homelabber quite nicely. Things like fs send and native encryption are big.
Compared to BTRFS, well, it's definitely an improvement in many areas for a driver that's in the kernel.
Sorry, I don't know if it is documented anywhere, but in summary the project started with bcache (block cache) from a single developer (Kent Overstreet A.K.A Evil Pie Pirate) in 2010 that explained he was building a module for the Linux Kernel.
Bcache is a method of using a fast ssd drive as a caching mechanism for slow but large hdds. As is, the project was quite ambitious but then, when the developer was working in an evolution of bcache (kind-of lessons learned re-implementation), the project grew into a general-purpose POSIX filesystem.
Considering the origins of the most popular file system implementations, expecting a single individual being successful creating a general-purpose one sounded over ambitious.
Then in 2013, out of the blue, Kent left Google to solely work in this project. (In reality though, he spent two years later in Datera as well.)
Then, how do you finance a single developer for a file system from 2013 onwards up to today, when it finally merged into the kernel?
Patreon. The whole thing was financed through it.
That said, there are other collaborators like Daniel Hill, Dave Chinner or Brian Foster, yet what's surprising is how this started as a side project and eventually became the main competitor of corporate-developed file systems by Patreon funding.
Note: A bit of hype-control here, btrfs which would be the main "competitor" was merged into kernel 14 years ago, so bcachefs still has a long way to go before we can trust it with our data.
Well yes, but seeing the history it has, I thought it would go through some more hiccups along the way, so it would actually take way more than that.
I'm glad to see I was wrong!