On Mon, Aug 24, 2009 at 11:19:01AM +0000, Florian Weimer wrote:
> > +* don't damage the old data on a failed write (ATOMIC-WRITES)
> > +
> > + (Thrash may get written into sectors during powerfail. And
> > + ext3 handles this surprisingly well at least in the
> > + catastrophic case of garbage getting written into the inode
> > + table, since the journal replay often will "repair" the
> > + garbage that was written into the filesystem metadata blocks.
>
> Isn't this by design? In other words, if the metadata doesn't survive
> non-atomic writes, wouldn't it be an ext3 bug?
So I got confused when I quoted your note, which I had assumed was
exactly what Pavel had written in his documentation. In fact, what he
had written was this:
+Don't damage the old data on a failed write (ATOMIC-WRITES)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Either whole sector is correctly written or nothing is written during
+powerfail.
+
+....
So he had explicitly stated that he only cared about the whole sector
being written (or not written) in the power fail case, and not any
other. I'd suggest changing ATOMIC-WRITES to
ATOMIC-WRITE-ON-POWERFAIL, since the one-line summary, "Don't damage
the old data on a failed write", is also singularly misleading.
- Ted
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