Comparing HAMMER And Tux3
(Thu, 07 Aug 2008 15:25:34 +0000)
"The big advantage Hammer has over Tux3 is, it is up and running and released in the Dragonfly distro," began Daniel Phillips, offering a comparison between the two filesystem. He continued, "the biggest disadvantage is, it runs on BSD, not Linux, and it so heavily implements functionality that is provided by the VFS and block layer in Linux that a port would be far from trivial. It will likely happen eventually, but probably in about the same timeframe that we can get Tux3 up and stable." This led into a lengthy and interesting technical discussion between Daniel and HAMMER author Matthew Dillon, comparing the design of the two filesystems.
Matthew reviewed the Tux3 notes and replied, "it sounds like Tux3 is using many similar ideas [as HAMMER]. I think you are on the right track. I will add one big note of caution, drawing from my experience implementing HAMMER, because I think you are going to hit a lot of the same issues. I spent 9 months designing HAMMER and 9 months implementing it. During the course of implementing it I wound up throwing away probably 80% of the original design outright." Daniel noted that he's been working on the Tux3 design for around ten years, "and working seriously on the simplifying elements for the last three years or so, either entirely on paper or in related work like ddsnap and LVM3." Matthew cautioned, "I can tell you've been thinking about Tux for a long time. If I had one worry about your proposed implementation it would be in the area of algorithmic complexity. You have to deal with the in-memory cache, the log, the B-Tree, plus secondary indexing for snapshotted elements and a ton of special cases all over the place. Your general lookup code is going to be very, very complex. My original design for HAMMER was a lot more complex (if you can believe it!) then the end result. A good chunk of what I had to do going from concept to reality was deflate a lot of that complexity." The friendly conversation offers a very detailed look at the design choices made in each of these file systems.