Topic: what is journaling?

"Matthew Dillon has made significant progress on DragonFly's journaling code, which can now mirror partitions. Essentially all that remains now is for the "reverse journaling" work to be completed (allowing for filesystem rollback), and for stability to be increased"

what does this mean in english, I want to know what this feature is

For example, Linux had at least two completely independent USB stacks before Linus Torvalds rejected them both and wrote a third one from scratch, after he found both existent Linux  stacks unsatisfactory.  (When pressed for an explanation as to why he selected the API he did, Torvalds stated: "because I wanted to."

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Re: what is journaling?

Wikipedia has a nice description of journaling at http://en.wikipedia.org/wiki/Journaling_file_system

What's being added in DragonFly, however is a bit different than the traditional meaning of journaling. Traditional journaling provides in summary a "fast crash recovery" feature, and the implementation is filesystem-dependent. DragonFly, on the other hand, has a jounaling layer in the kernel, which as I understand it is placed "above" the VFS layer, which in simple terms means you can "send the data somewhere else", besides writing it to disk.

This would allow for real-time mirroring of data, even to remote disks, or to send the data to some intermediary process which could scan it for, say, audit purposes, etc.. there are many possibilities. One of the intended features is to also provide data rollback to arbitrary points in the disk "history".

I believe there is another dfly developer working on traditional journaling for UFS, but I don't know what's the status of that.