On Sat, Sep 15, 2018 at 6:23 AM Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > On Fri, Sep 14, 2018 at 05:06:44PM +0800, 焦晓冬 wrote: > > Hi, all, > > > > A probably bit of complex question: > > Does nowadays practical filesystems, eg., extX, btfs, preserve metadata > > operation order through a crash/power failure? > > Yes. > > Behaviour is filesystem dependent, but we have tests in fstests that > specifically exercise order preservation across filesystem failures. > > > What I know is modern filesystems ensure metadata consistency > > after crash/power failure. Journal filesystems like extX do that by > > write-ahead logging of metadata operations into transactions. Other > > filesystems do that in various ways as btfs do that by COW. > > > > What I'm not so far clear is whether these filesystems preserve > > metadata operation order after a crash. > > > > For example, > > op 1. rename(A, B) > > op 2. rename(C, D) > > > > As mentioned above, metadata consistency is ensured after a crash. > > Thus, B is either the original B(or not exists) or has been replaced by A. > > The same to D. > > > > Is it possible that, after a crash, D has been replaced by C but B is still > > the original file(or not exists)? > > Not for XFS, ext4, btrfs or f2fs. Other filesystems might be > different. Thanks, Dave, I found this archive: https://www.mail-archive.com/linux-btrfs@xxxxxxxxxxxxxxx/msg31937.html It seems btrfs people thinks reordering could happen. It is a relatively old reply. Has the implement changed? Or is there some new standard that requires reordering not happen? > Cheers, > > Dave, > -- > Dave Chinner > david@xxxxxxxxxxxxx
