BetrFS: A Right-Optimized Write-Optimized File System

Here're what I found on the idea of adding buffers to branch nodes. L. Arge described the Buffer Tree idea in 1995 with (a,b)-Tree for other data structures. Brodal and Fagerberg formalized it for B+Tree in 2003. There's also the more modern Bε-Tree, the B-epsilon Tree, with similar idea, used in the BetrFS file system and various DBs. Tokutek built TokuDB using a similar idea and called it Fractal Tree (which was derived from Bε-Tree). Hitchhicker Tree is the append-only version of Fractal Tree, similar to the append-only B+Tree. * L. Arge. The buffer tree: A new technique for optimal I/O-algorithms. In Proc. 4th Workshop on Algorithms and Data Structures (WADS), volume 955 of Lecture Notes in Computer Science, pages 334–345, Springer Verlag, Berlin. 1995. link * G. S. Brodal, R. Fagerberg. Lower Bounds for External Memory Dictionaries. 2003. link * Bε-Tree, link , ▶ this video . An Introduction to Bε-trees and Write-Optimization, link , link * Tokutek. How Fractal Trees Work. 2011. link * Hitchhiker Tree. 2016. link

> here's a talk given by Rob Johnson a few years ago at Microsoft Research: BetrFS: A Right-Optimized Write-Optimized File System ▶ this video Interesting talk, I wonder how much of the perf. advantage diminishes in a finished, production-ready implementation though. Comparing an 80%-complete R&D prototype mule against crash-resilient posix-compliant production filesystems is basically never a fair perf. comparison. You might find that just implementing rename and hard-links properly alone is going to kill your perf. since you dispensed with on-disk inode equivalents. Nice to see people poking at these issues nonetheless, Linux needs better filesystem options.

The website doesn't seem to mention that several of the papers on the filesystem won best-paper awards at major conferences. The paper, Optimizing Every Operation in a Write-Optimized File System, in particular, won best-paper award at FAST '16. Also, if you're interested in learning more about B^\epsilon trees, here's a talk given by Rob Johnson a few years ago at Microsoft Research: BetrFS: A Right-Optimized Write-Optimized File System ▶ this video In general, I think it's really cool that there is a file system that exists today (i.e., BetrFS) that uses data structures which didn't exist 25 years ago. It's a great example of theoreticians and systems researchers working together.

This isn't completely fair, although most of it is. Some of the reasons for modifying Linux are performance enhancements to the filesystem layer that only make sense with a Bε-tree filesystem (and are not possible without patching Linux). They cover this in the hour-long talk at MS research linked elsewhere in this thread.[1] (Yes, it's long, but it's a pretty good presentation.) E.g., they describe modifying the page cache to write-through small modifications to file data, rather than dirtying the entire page and writing it back later (a form of write amplification). [1]: ▶ this video

Talk given by Rob Johnson [1] at MSR a few years back... BetrFS: A Right-Optimized Write-Optimized File System ▶ this video [1] link

This reminded me of BetrFS presented at FAST 15. It looks like there's a more up to date presentation online[1] where the delete performance issues have been fixed. [1] ▶ this video