"HAMMER work is still progressing well, I hope to have most of it working in a degenerate single-cluster (64MB filesystem) case by the end of next week. (cluster == 64MB block of the disk, not cluster as in clustering)," noted Matthew Dillon on the DragonFlyBSD mailing list. He continued, "gluing the per-cluster B-Tree's together for the multi-cluster case is turning out to be more of a headache and will probably take at least 2 weeks to get working. Some fairly sophisticated heuristics will be needed to avoid unnecessary copying between clusters." Matt went on to note that the next DragonFlyBSD release will likely be delayed a month:

"I may decide to move the 2.0 release to mid-January to give myself some more time. This is similar to what we did for 1.8. Also, I think a January release is better then a Christmas release because people get busy with christmas-like things. I want the filesystem to be at least beta quality as of the release and I don't think its possible to get it there by mid-December."

"Speaking of on-disk B-Trees, ReiserFS' biggest problems are all based on its use of flexible B-Trees," suggested a reader on the DragonFlyBSD Kernel mailing list, pointing to the difficulty of detecting a failed node and then of rebuilding the B-Tree. HAMMER filesystem designer and author, Matt Dillon, explained, "if a cluster needs to be recovered, HAMMER will simply throw away the B-Tree and regenerate it from scratch using the cluster's record list. This way all B-Tree I/O operations can be asynchronous and do not have to be flushed on fsync. At the same time HAMMER will remove any records whose creation transaction id's are too large (i.e. not synchronized with the cluster header), and will zero out the delete transaction id for any records whos deletion transaction id's are too large." Matt then acknowledged:

"The real performance issue for HAMMER is going to be B-Tree insertions and rebalancing across clusters. I think most of the issues can be resolved with appropriate heuristics and by a background process to slowly rebalance clusters. This will require a lot of work, though, and only minimal rebalancing will be in [the end-of-the-year] release."