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"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.

"Hurrah! 2.0 has been released!" said Matthew Dillon, announcing the eighth major release of DragonFly BSD. This release is the first to include HAMMER, a new clustering filesystem that already boasts an impressive list of features, including: "crash recovery on-mount, no fsck; fine-grained snapshots, snapshot management, snapshot-support for filesystem-wide data integrity checks; historically accessible by default; mirroring: queueless incremental mirroring, master to multi-slave; undo and rollback; reblocking; multi-volume, maximum storage capacity of 1-Exabyte." Other highlighted changes in this release include, "native fairq-queue implementation using ALTQ, for PF", and "native connection state recovery to PF, so router reboots do not drop active TCP connections."

Matthew Dillon continues to make significant progress on his HAMMER clustering filesystem for DragonFly BSD. He labeled the latest release 56c, noting that it, "represents an additional significant improvement in performance, [also including] bug fixes and most of the final media changes." A significant improvement in write performance was obtained by making the filesystem block size automatically increase from 16K to 64K when a file grows to larger than 1 MB. One remaining media change is required to optimize mtime and atime storage, at which point HAMMER will go into testing and bug fixing mode. Matt noted, "HAMMER's performance is extremely good now, and its system cpu overhead has dropped to roughly the same that we get from UFS", adding, "HAMMER is now able to sustain full disk bandwidth for bulk reads and writes.

"HAMMER makes no modifications to the B-Tree whatsoever on the front-end. When you create, delete, rename, write, etc... when you do those operations HAMMER caches them in a virtualization layer in memory and doesn't make any modifications to its on-media data structures (or their in-memory representations) at all until the meta-data is synced to disk," DragonFly BSD creator Matthew Dillon explained, comparing HAMMER, his clustering filesystem, to a wiki summary of Reiser4's implementations. He continued:

"After another round of performance tuning HAMMER all my benchmarks show HAMMER within 10% of UFS's performance, and it beats the shit out of UFS in certain tests such as file creation and random write performance," noted DragonFly BSD creator Matthew Dillon, providing an update on his new clustering filesystem. He continued, "read performance is good but drops more then UFS under heavy write loads (but write performance is much better at the same time)." He then referred to the blogbench benchmark noting, "now when UFS gets past blog #300 and blows out the system caches, UFS's write performance goes completely to hell but it is able to maintain good read performance." Matthew then compared this to HAMMER:

Matthew Dillon sent out a series of updates about his developing HAMMER filesystem, noting that he is currently focusing on the reblocking and pruning code, tracking down a number of bugs resulting in B-Tree corruption. He also noted that previously HAMMER was comprised of three components: B-Tree nodes, records, and data. In his latest cleanups, he has entirely removed the record structure, "this will seriously improve the performance of directory and inode access." This change did require an on-media format change, "I know I have said this before, but there's a very good chance that no more on-media changes will be made after this point. The official freeze of the on-media format will not occur until the 2.0 release, however."

"HAMMER is going to be a little unstable as I commit the crash recovery code," began DragonFly BSD creator Matthew Dillon, adding, "I'm about half way through it." He went on to list what's left for crash recovery to work with HAMMER, his new clustering filesystem, "I have to flush the undo buffers out before the meta-data buffers; then I have to flush the volume header so mount can see the updated undo info; then I have to flush out the meta-data buffers that the UNDO info refers to; and, finally, the mount code must scan the UNDO buffers and perform any required UNDOs." He continued: "The idea being that if a crash occurs at any point in the above sequence, HAMMER will be able to run the UNDOs to undo any partially written meta-data. HAMMER would be able to do this at mount-time and it would probably take less then a second, so basically this gives us our instant crash-recovery feature."

"I have a question for the PF/ALTQ masters out there," Matthew Dillon began on the DragonFlyBSD kernel mailing list, having recently switched from using a Cisco router to a DragonFlySD server running PF. "I am trying to configure PF in a manner similar to what Cisco's fair-queue algorithm does. Cisco's algorithm basically hashes TCP and UDP traffic based on the port/IP pairs, creating a bunch of lists of backlogged packets and then schedules the packets at the head of each list." He went on to explain that he was unsuccessfully trying to configure the same thing with PF, "neither CBQ nor HFSC seem to work well. I can separate certain types of traffic but the real problem is when there are multiple TCP connections that are essentially classified the same, and one is hogging the outgoing bandwidth. So the question is, is there a PF solution for that or do I need to write a new ALTQ mechanic to implement fair queueing?"

Matthew Dillon posted on update on his evolving HAMMER filesystem, noting that it "passes all standard filesystem stress tests and buildworld will run with a HAMMER /usr/obj". He also noted, "pruning and reblocking code is in and partially tested, but now needs more stringent testing; full historical access appears to be working but needs testing." He added, "there are two big-ticket and several little-ticket items left. HAMMER will officially go Alpha when the big-ticket items are done, and beta when we get a few of the little-ticket items done." The two "big-ticket" items left to be completed are UNDO crash recovery code, and handling for full filesystems. Matt summarized:

"Hello everyone! We are happy to say that the 1.12 release is now available!" began Matthew Dillon, announcing the latest stable version of DragonFly BSD. The project's home page explains, "DragonFly is an operating system and environment originally based on FreeBSD. DragonFly branched from FreeBSD in 2003 in order to develop a radically different approach to concurrency, SMP, and most other kernel subsystems." Regarding the latest release, Matt explained: "This release is primarily a maintenance update. A lot of work has been done all over the kernel and userland. There are no new big-ticket items though we have pushed the MP lock further into the kernel. "The 2.0 release is scheduled for mid-year. Of the current big-ticket item work, the new HAMMER filesystem is almost to the alpha stage of development and is expected to be production ready by the mid-year 2.0 release." read more

"HAMMER won't be ready for sure (things take however long they take), but the hardest part is working and stable and I'm just down to garbage collection and crash recovery," noted Matthew Dillon, discussing the status of what is ultimately intended to be a highly available clustering filesystem. The upcoming DragonFlyBSD release this month was originally intended to be 2.0 with a beta quality HAMMER, but the decision was recently made to call the release 1.12 while HAMMER continues to stabilize. Matt continued, "HAMMER is really shaping up now. Here's what works now: all filesystem operations; all historical operations; all Pruning features". During the discussion, he was asked how he planned to support multi-master replication, in reply to which he began:

"Work continues to progress well but I've hit a few snags," noted Matthew Dillon, referring to the ongoing development of his HAMMER filesystem. He began by highlighting a number of problems with the current design, then adding, "everything else now works, and works well, including and most especially the historical access features." He continued: "I've come to the conclusion that I am going to have to make a fairly radical change to the on-disk structures to solve these problems. On the plus side, these changes will greatly simplify the filesystem topology and greatly reduce its complexity. On the negative side, recovering space will not be instantaneous and will basically require data to be copied from one part of the filesystem to another."

"HAMMER is progressing very well with only 3-4 big-ticket items left to do," noted DragonFlyBSD creator Matthew Dillon regarding the ongoing development of his highly available clustering filesystem, "I'm really happy with the progress I'm making". He listed "on-the-fly recovery, balancing, refactoring of the spike code, and retention policy scan" as the remaining items needing to be implemented. "everything else is now working and reasonably stable. Of the remaining items only the spike coding has any real algorithmic complexity. Recovery and balancing just require brute force and the physical record deletion. The retention policy scan needs is already coded and working (just not the scan itself)."

"HAMMER is progressing well. The filesystem basically works, but there are some major pieces missing such as, oh, the recovery code, and I still have a ton of issues to work through... the poor fs blows up when it runs out of space, for example, due to the horrible spike implementation I have right now," DragonFlyBSD creator Matthew Dillon stated. HAMMER is a new highly available clustering filesystem aimed to be of beta quality by the DragonFlyBSD 2.0 release later this month. Matt notes, "It isn't stable yet but some major milestones have been achieved. I am able to cpdup, rm -rf, and perform historical queries on deleted data." Matt went on to caution, "please note that HAMMER is *NOT* yet ready for wider testing. Please don't start reporting bugs yet, because there are still tons of things for me to work through." read more

"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."