Re: 2.6.36 io bring the system to its knees

[Dave Chinner <david@fromorbit.com>]

On Sun, Nov 07, 2010 at 07:50:13AM -0800, Linus Torvalds wrote:
> On Sun, Nov 7, 2010 at 4:08 AM, Jens Axboe <axboe@kernel.dk> wrote:
> >
> > As already mentioned, ext3 is just not a good choice for this sort of
> > thing. Did you have atimes enabled?
> 
> At least for ext3, more important than atimes is the "data=writeback"
> setting. Especially since our atime default is sane these days (ie if
> you don't specify anything, we end up using 'relatime').
> 
> If you compile your own kernel, answer "N" to the question
> 
>   Default to 'data=ordered' in ext3?
> 
> at config time (CONFIG_EXT3_DEFAULTS_TO_ORDERED), or you can make sure
> "data=writeback" is in the fstab (but I don't think everything honors
> it for the root filesystem).

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....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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