A ‘dirty’ vnode is a disk data reference that has changed but hasn’t yet been committed to disk. This pair of commits adds a syncing threshold, useful for anyone with slower disk resources. Remember, disks lie.
HAMMER1, mounted and unmounted cleanup
The regular maintenance scripts for HAMMER1 assume that it’s mounted at the time of cleanup. If you have them unmounted, they won’t go through that regular maintenance, but it’s easy enough to fix.
Hammerception
You could, if you are running DragonFly-current, create a vkernel using HAMMER2, and try out HAMMER2 even if your underlying disk is HAMMER1. Odd, but useful.
Creating HAMMER2 volumes on Linux
You can make them, but you can’t mount them. Tomohiro Kusumi’s note that mkfs_hammer2 works on Linux is of little wide practical use, but it’s a sign of progress to a larger goal.
HAMMER1, on Linux
Tomohiro Kusumi has made the userspace tools for HAMMER1 compilable on Linux, so you could create a HAMMER1 volume on a Linux system. No, it’s not the ability to read/write HAMMER1 in Linux, unfortunately – just some manipulation of volumes. I don’t know what his future plans are for HAMMER1|2 on Linux, if any.
HAMMER2 in the installer
HAMMER2 is now available by default in DragonFly, and can be used in the installation process. (It was possible, but manual, before.) The next DragonFly release should be soon.
HAMMER2 hardlinks, other work
Matthew Dillon’s found a solution to the problem of hardlinks in HAMMER2, and so moved on to dirents. The design document has a significant update to match.
HAMMER version 7
Continuing my catchup on recent commits, there’s now a ‘version 7’ internal to HAMMER 1. It changes the CRC code to a faster version, but since this instruction isn’t used (yet), there’s no real world impact. Remember this for next time you want to run ‘hammer version-upgrade’.
Mount and HAMMER2 labels
If you’re mounting a HAMMER2 filesystem, you can refer to it by label instead of by device.
No, it’s not ready for use yet and I don’t have a date other than “when it’s done”, to preanswer the next questions.
Hammer and PFS notes
Simple fix for speed
I always attributed speed issues to writing transaction history, but: Matthew Dillon discovered HAMMER was repeating itself when writing to disk. Fixing that issue doubled write speed. This fix is in 4.6 and the upcoming release.
Good news for multiple processors
Matthew Dillon has made a number of locking improvements, that speeds up performance on systems with multiple processor. Here’s his commit with some numbers. Note that he’s testing with these built-in utilities. This probably helps multiple cores too, and some attention is shown to Hammer, too.
Zeroing does nothing
This makes sense once you think about it: copy-on-write filesystems (like Hammer2 and ZFS and probably others) actually do nothing when “zeroing” out filespace.
Buildworld for -current users
If you are on DragonFly-current, AKA DragonFly 4.7, make sure to perform a full buildworld on your next upgrade. Tomohiro Kusumi changed a Hammer ioctl, and the buildworld is needed to keep everything in sync.
Reminder: move your Hammer cleanup
A useful tip: if your DragonFly machine isn’t usually on 24/7 (e.g. a laptop, not a server), you should move your Hammer cleanup from 3 AM to sometime when the computer is normally on.
Hammer2 major changes
Hammer2 now has inode indexing, which Matthew Dillon was avoiding while trying to create more efficient hardlink support. The result is now with that problem solved, more updates can come in: NFS support, mtime updates, output changes, code removal, and lots of other changes, not all of which I’m even linking.
What’s that @@?
Tomohiro Kasumi wrote a lengthy explanation of what “@@” means, in the context of the Hammer file system. It acts as a sort of signifier for each actual Hammer pseudo-file-system, since it’s possible to null-mount these anywhere in DragonFly, under all sorts of names. Don’t trust my summary, though – read his.
The rescue undo
Did you know there’s a rescue image, created with crunchgen, in DragonFly? If your system can boot to single-user mode, you can use it to at least manipulate data on disk – it includes mined as a simple small editor. (Since vi assumes /usr is mountable.) This rescue image now includes undo, so you can back out changes on a Hammer volume.
Hammer and FreeBSD
Tomohiro Kusumi would like to port Hammer (1) to FreeBSD, as noted in this bug discussion. It’s not even begun to happen, but if you can contribute, please do.
More Hammer fixups
Tomohiro Kusumi has been creating a near-constant stream of bugfixes and cleanups to Hammer for quite some time. I don’t often link to it, because they are incremental improvements and hard to linkblog, so to speak. In an effort to make up for this deficit, I do want to draw attention to his two recent commits: “Make hammer commands print root volume path“, and “Print volume list after volume-add|del“. Small changes, but this is what makes complex systems usable.