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 Thus, B is either the original B(or not exists) or has been replaced by A. 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 Is it possible that, after a crash, D has been replaced by C but B is still 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. Cheers, Dave, -- Dave Chinner david@xxxxxxxxxxxxx
