lkml.org 
[lkml]   [2018]   [Sep]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: metadata operation reordering regards to crash
On Sat, Sep 15, 2018 at 6:23 AM Dave Chinner <david@fromorbit.com> 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 Thus, B is either the original B(or not exists) or has been replaced by A.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 Is it possible that, after a crash, D has been replaced by C but B is still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@vger.kernel.org/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@fromorbit.com

\
 
 \ /
  Last update: 2018-09-15 08:59    [W:0.064 / U:0.772 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site