User feedback: raise the default leaf size to 16k

["Holger Hoffstaette" <holger.hoffstaette@googlemail.com>]

Hi,

after using btrfs with 3.7.x and default settings without any problems so
far (knock on wood!) I had to redo a 1TB filesystem and this time decided
to try two small changes:

- raise the leaf size to 16k
- use single metadata profile

After restoring the contents (~300GB, mix of large and small files) the
difference in behaviour on a single disk is *very* noticeable.
Therefore I want to suggest changing the default values accordingly. IMHO
the new behaviour - maybe including the single metadata redundancy - is
much more in line with behaviour that people expect out of the box. I
believe many cases where users report degrading performance over time can
be attributed to this. Whether single metadata is too much of a risk I
cannot judge, but please at least raise the default leaf size.

Just my 0.01€ of user feedback :)

thanks
Holger