Re: [Fwd: Re: here i come !]

[Miles Lane <miles megapathdsl net>]

On Mon, 2002-06-24 at 18:47, Seth Nickell wrote:
> > Also, I think that the user should know what he is doing when he sets it
> > to be ext2, we never want a user to run it without activily choosing it
> > (imho anyway). Yes, it will eat more battery if you run ext3 on your
> > laptop *BUT* you will not face an 'fsck' at boot.
> > 
> > We can have a document describing how to use 'ext2' together with
> > information about pros and cons, but I think we should always go with
> 
> As Nielsen (I think) quips, "Users can't read, and even if they could,
> they wouldn't want to"
> 
> Don't rely on documentation. Most users simply don't read it. If there's
> an important distinction like this (which we've readily identified: use
> ext3 unless its a laptop in which case journalling is probably too
> costly) we either need to get the filesystem fixed (that'd sure be nice,
> I've heard there are patches that help immensely with this) or we need
> to handle the choice of filesystem automaticall, preferably *not*
> exposing the choice to the user.

I asked about this on LKML.  I'll include the response, since it
was informative.  Before I get to that, my lastest thinking is that
if we can simply tweak the EXT3 filesystem to do the right thing
depending on whether or not there is wall power, then that seems
like the obviously right way to go.  From the response I got, it
looks like this is possible.

------------------------

                             From: 
Andreas Dilger
<adilger clusterfs com>
                               To: 
Miles Lane <miles megapathdsl net>
                               Cc: 
LKML <linux-kernel vger kernel org>
                          Subject: 
Re: Automatically mount or remount
EXT3 partitions with EXT2 when a
laptop is powered by a battery?

On Jun 24, 2002  13:02 -0700, Miles Lane wrote:
> Hi,
> 
> Is there any possibility we could:
> 
> 1)  Add support to the boot/mounting process 
>     so that, if a machine is being powered by
>     battery, EXT3 partitions are mounted with
>     EXT2, instead?

Impossible right now.  While the on-disk format is the same, the
ext2 and ext3 drivers are totally different.

It's like asking if you can switch between IDE and SCSI drivers
automatically for a disk when you go on battery.
 
That said, it would be possible to update the ext3 code to allow it
to mount a filesystem without a journal by updating the journal
wrappers in include/linux/ext3_jbd.h.

Even so, the reasoning you give is a bad one - you are far safer
with ext3 on your laptop when it is running out of batteries,
because you are likely to run out of battery without unmounting
the filesystem cleanly, and that's just when you want ext3.

You should just change the flush parameters to be longer, or
figure out exactly why ext3 is writing stuff to disk when there
is no real I/O happening.