On Mon 07-02-11 08:35:31, Andreas Dilger wrote:

On 2011-02-07, at 08:19, Jan Kara wrote:

quoted

On Fri 04-02-11 10:36:21, Andreas Dilger wrote:

quoted

The question is whether we need to mimic the runtime behavior or just the
on-disk format?  Apps already need to deal with ext4 and other fs that do
not do ext3 ordered mode.

 Well written apps do, but badly written apps don't and e.g. our distro
customers don't always have the choice of the application. So as a developer
I see your point (screw stupidly written apps) but in the real world, I'm
afraid it's too hard on users.

We have to remember that this is only for new kernels, and does not
affect older kernels or existing applications, so such users shouldn't be
affected.

  Well, customers do upgrade distros and that means they get new kernels
but still they are bound to use the same app from their ISV so I don't
think there won't be users hitting this.

quoted

quoted

I think the best road forward is to make ext4 the default for ext2 and
ext3 filesystems in newer kernels, and mark ext2 and ext3 obsolete. This
will start to get usage and testing of these other config options. The
ext2 mode is already heavily tested at Google, and don't they also test
noextent mode on updated filesystems, or were all of the filesystems
reformatted with ext4 options?

 Yes, I know you are on relatively radical side ;). My position would be
to test ext4 for resonable combinations of options as ext2 driver and if
that works, switch ext2 as you describe. Then if it works fine for an year
or so, we can talk about ext3 but as James said, ext3 is still widely used
so there might be more friction on subtle runtime differences...

Since most new distros use ext4 by default, the point is kind of moot,
because those users will get this behaviour in any case.  Relatively few
users upgrade their kernel on a production system after it is installed,
except for errata kernels, and I definitely wouldn't expect such a change
to appear in an errata kernel.

Umm, lot of our customers upgrade even production systems (e.g. SLE10 SP3
-> SLE11 SP1 these days). But still, they keep the old filesystem (they do
not reformat their storage) because they were happy with how it worked. And
yes, they are happy about things that get better but loudly complain about
things that got worse for them.

Of course this does not have a perfect solution (someone will always
complain ;) but putting reasonable effort into making behavior of ext4
in the 'compatibility' mode not too much different from ext3 is IMHO decent
to users.

									Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR