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Re: [RFC] Support for using multiple CDs during installation



Your mail seriously put me off for a few days, so I've given myself some 
extra time to think about it.

On Friday 26 October 2007, Joey Hess wrote:
> > As argued above, loading multiple CDs in no way conflicts with using a
> > mirror. IMO we have to always ask both questions.
>
> Neither does installing lilo to one disk and grub to another, but d-i
> does not prompt the user to choose if they want to use lilo, and follow
> that up with a separate prompt about whether to use grub. Instead d-i
> allows the -0.00001% of users who need to do this to use the menu in
> expert mode.

OK, but in your proposal the option to scan additional CDs is _not asked at 
all_ if they choose to use a mirror. A significant difference I'd say.

I also still feel that having to say "no" to a mirror is in any way logical 
if you want to use additional CDs, so we'd have to add some sort of ugly 
(conditional!) explanation in the use mirror dialog about that.

> > Also, first letting the user scan all CDs and then asking about adding
> > a mirror is a lot more logical than the other way around:
> > a) it seems not very natural to first scan the installation CD, then do
> > other stuff, and then go back to scanning CDs
>
> Scanning the first CD doesn't involve the user doing something, so most
> users will not particularly notice it's happened.

It still is visible for users who pay attention and it is also visible 
because of the way the mirror question is phrased.

> > b) it is much more natural to have a user consider:
> > - "OK, I've now scanned this huge pile of CDs; do I still want to use a
> >    mirror in addition to that or not?"
>
> No, it's much more natural to optimise for the common case, which is
> using a mirror.

I don't think adding a single question that is only asked when it is 
relevant and has a default of "no" is a loss of optimization.
I also think that a lot more users would like to be able to scan additional 
CDs than you think. Not everybody in the world has broadband.

> Users should not be encouraged to scan huge piles of CDs. 
> Huge piles of CDs are obsolete in all but a very few edge cases.

I know your aversion against the full CD sets. I remember your blog about 
it. But I don't think scanning additional CDs if you already have them is 
in any way harmful.

I also don't think my changes "encourage them" as:
- the question is only asked when there is a real possibility the user
  may have additional CDs available
- the default of the question is "no" which is an indication that you
  don't absolutely need additional CDs; the question also includes the
  qualification "if available"

I also very much doubt users who are at this stage of the installation and 
don't have multiple CDs will suddenly decide to break off the install and 
rush off to download/buy the full set and start the install over.

I agree that downloading/buying/scanning a full set of CDs is silly in 
almost all cases. However, if you want to do something about that it should 
be done where users decide to *buy or download* the images: on the website 
and in documentation.
What your proposal here does is punishing users who already have multiple 
CDs (and hopefully a lot will probably only have a limited number instead 
of the full set anyway) by hiding the question behind an unrelated other 
question and thus effectively not making the option available at all.

> Prompting for additional CDs will make the user feel that he should
> provide them, which is typically a waste of his time and leads to a
> system that is less functional (because apt asks you to switch CDs all
> the time). Or more likely, it will make the user worry that he doesn't
> have more than one CD.

Nonsense. I'm perfectly willing to clarify this in the dialog (or maybe 
better in an additional dialog after the user has chosen yes), but I 
completely disagree with this. See above.

> > than:
> > - "hey, they're asking me if I want to use a mirror; do I need one? I
> >    probably do as apparently I cannot use this shitload of CDs they let
> >    me download and burn..."
>
> When a user downloads a bunch of CDs they don't neeed, as in your
> example, we've already failed once, let's not fail twice.

Let's not punish them either if they've already done so...

> In general, you seem to be assuming that using multiple CDs is something
> other than an exceptional edge case. It is not. That's why I happily
> dropped it from the etch installer, and why only a few users have missed
> it.

On the other hand, we've listed the lack of support as a "known issue" and 
we've had it high on our TODO list. A fair number of installation reports 
has mentioned it as something that was missing.

And, as said before, I think it is wanted a lot more than you think. Not for 
full sets, but I think for a lot of users downloading the first 2-4 CDs can 
be a very sensible option. Consider for example the PowerPC case where CD1 
hardly contains anything beyond the base system.
And I've argued in my earlier mail that there is no reason why such users 
should not be allowed to use a mirror in combination with those CDs.

> If you want to fill in that edge case in the installer, that's fine
> (and impressive), but it's not good to complicate the installation
> process for the common case when doing so.

Adding a single, focussed question with a default of "no" is not
"complicating the common case".

I'm still convinced that my implementation is the cleanest one possible. It 
is focussed, has conservative defaults and it respects the relative 
independence of the generators.
I'm willing to discuss changes, but hiding the option to use CD sets behind 
the use mirror question is not an option for me.

Cheers,
FJP

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