CD optimization

[Matt Zimmerman]

I had to do a couple of installs in order to debug #1143, and along the way,
I started to take an interest in the time taken by archive-copier.  It seems
that by the time archive-copier runs, the data loaded into cache by
cdrom-detect has been lost, because I see the same slow seeking behaviour as
I saw previously with debootstrap.

So, on a second round, I ran a "while true; do find /cdrom/ >/dev/null;
sleep 1" on console #2.  This held the data in cache, avoided all of the
seeking I was seeing, and subjectively sped up both debootstrap and
archive-copier by a good margin.

Therefore, it would appear that the idea has great potential, but that we're
not successfully exploiting it yet.  The approach I used above seems awfully
heavy-handed, but I don't immediately see any other way to coerce this stuff
to stay in cache.  Any ideas?

-- 
 - mdz