Re: 2.6.36 io bring the system to its knees

[Dave Chinner <david@fromorbit.com>]

On Wed, Nov 10, 2010 at 11:08:17AM +0300, Evgeniy Ivanov wrote:
> On Wed, Nov 10, 2010 at 4:32 AM, Dave Chinner <david@fromorbit.com> wrote:
> > Don't forget to mention data=writeback is not the default because if
> > your system crashes or you lose power running in this mode it will
> > *CORRUPT YOUR FILESYSTEM* and you *WILL LOSE DATA*. Not to mention
> > the significant security issues (e.g stale data exposure) that also
> > occur even if the filesystem is not corrupted by the crash. IOWs,
> > data=writeback is the "fast but I'll eat your data" option for ext3.
> >
> > So I recommend that nobody follows this path because it only leads
> > to worse trouble down the road.  Your best bet it to migrate away
> > from ext3 to a filesystem that doesn't have such inherent ordering
> > problems like ext4 or XFS....
> 
> Is it save to use "data=writeback" with ext4?

I believe the same issues exist with data=writeback in ext4, but you
probably should have an ext4 developer answer that question for
certain.

> At least are there security issues?
> Why do you say, that fs can be corrupted? Metadata is still
> journalled, so only data might be corrupted, but FS should still be
> consistent.

Data corruption is still a filesystem corruption.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com