[Sugar-devel] Hello, was Re: Hack to get a USB/SD to autologin to only "Sugar-desktop on a stick". from a F12-alpha live CD

[Douglas McClendon]

Douglas McClendon wrote:
> David Farning wrote:
>>
>> The primary use case is now running Sugar and the underlying OS as
>> natively as possible on the removable solid state media.  The primary
>> goals are now reliability and speed.
>>
>> The issue is not that overlays are bad/good or real file systems.  The
>> issue is, can SoaS improve stick reliable  and speed by eliminating
>> the overlays and writing the _contents_ of the overlay directly onto
>> the solid state device using a file systems which is aware of the
>> design characteristics of current generations of USB keys.
> 
> One would certainly expect this to be the case at some point if not 
> already, and it looks like you are deep into the task of figuring out 
> exactly when that point is and what it looks like.
> 

Yeah, this is all pretty nastily complex.  I just reread the above two 
paragraphs, and think that in my reply I misunderstood the 2nd paragraph.  But 
there is possible contradiction with the 1st paragraph.

I now see what you are saying in the 2nd paragraph, as the overlay living in a 
filesystem that does wearleveling/circular-writing(ish kind of stuff).  Which 
is different than what I previously thought you meant, i.e. having a 
traditional rootfs (no overlay), on a filesystem that does 
wearleveling/circular writing.  I.e. my vague semi-osmotic understanding is 
that btrfs's 'copy on write' feature has something to do with more or less 
always writing new data in a 'circular' fashion on disk, which is a kind of 
wear leveling, and can possibly facilitate interesting snapshot feature stuff. 
  I could however be way off.

And I guess I can conceive of a justification for putting the just the overlay 
on such a filesystem.  I.e. while the filesystem may not be ready for primetime 
as a rootfs, its ability to do the right thing(tm) vis-a-vis wearleveling on 
just the single readwrite overlay file, might be worth doing.


-dmc