On Wed, Nov 11, 2009 at 1:16 PM, Ted Unangst <ted.unan...@gmail.com> wrote: > On Tue, Nov 10, 2009 at 10:50 PM, Nick Guenther <kou...@gmail.com> wrote: >> See, since it seems that BSD doesn't have this file-data consistency >> guarantee, are Linus' worries about ext4's potential data loss just >> being alarmist? It seems to me that the case described in >> https://bugs.edge.launchpad.net/ubuntu/+source/linux/+bug/317781/comments/45 >> is just as likely to happen on OpenBSD--if I run KDE or GNOME and mess >> around with my settings then quickly murder the system the files will >> be resurrected empty, right? > > Yes, if you cut power before things are written to disk, they will not > be written to disk. Snark aside, it really is that simple. Different > filesystems have different definitions of what "written to disk > means", or more accurately, *when*, but in all cases, if you cared you > used fsync or tried a little harder to not crash. > >> What is the reason softdep isn't on by default? > > It changes the "expected" behavior. FFS without softdep is a lot > closer to the semantics people and most applications expect. >
Okay, one last question: one of the original softdep papers (http://www.usenix.org/publications/library/proceedings/bsdcon02/mckusick.htm l) is all about how softdeps can avoid fsck, but I just set softdep on all my filesystems, rebooted (to start fresh), wrote some files, wrote some more files, edited the first files, and jacked the power plug right after it said "wrote". When the system came up fsck ran, what gives? Does OpenBSD only implement softdep for the write speedups? I'm just really confused about what softdep -is- I guess. What semantics get changed? Do all the BSDs use the same softdep code? Did they pick and choose ideas from the original softdep papers? Thanks for letting me pick your brain, Ted, -Nick
