Messages in this thread | | | Date | Tue, 26 Oct 1999 15:24:25 -0500 | From | Brian Grayson <> | Subject | Re: Question on FFS support |
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On Sat, Oct 09, 1999 at 04:31:55AM -0400, Anthony Barbachan wrote: > > > included in the Linux kernel. I would have thought that with the need > for a > > > journaling filesystem FFS would have been adopted, especially with the > BSD > > > code available. Is there some issue that has prevented this? > > > > a) FFS is not journaling. ... > > c) FFS under FreeBSD uses Kirk's softupdates. That's what you ar thinking > > about. > > And softupdates is what gave me responder his quick fsck time? Ok I > see. Thanks. > > > d) s-u is not fs-specific, at least between the FFS/UFS/EXT2
I don't know, but the original FreeBSD responder may have meant LFS, the log-structured filesystem, which the BSDs have recently revamped. It is a true journaling file system distinct from FFS/UFS, and not merely soft-updates on top of a traditional block-structured file system. With LFS, you always append on writes, rather than overwrite. Thus, writes are fast, and if the machine crashes, since the previous data has not been overwritten, you can recover quite quickly. Of course, with finite disks you need to do some garbage-collecting, but LFS does all of that for you, and also has some optimizations so that reads are still fast.
Cool concepts, since it is solving a different problem, like fast transaction support, than traditional filesystems. There are a bunch of filesystem papers on LFS by John Ousterhout, Margo Seltzer, Keith Bostic, and Kirk McKusick that provide more details -- look at the mount_lfs man page on any recent *BSD system for the exact references.
Brian Grayson (a NetBSD fan in his spare time) (Not speaking for Motorola, of course!)
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