Exactly how cheap is a branch?

[TrudiQuinntrudi at perforce.com]

Forwarding this for: Adam B. Feder <ab at sgi.com>

We need to branch our source code for a beta (and eventually
a release).  I'm trying to decide if we should branch all
of /depot/mainline/ to /depot/ourbeta/ or if we should branch
individual subdirectories.  There are about 30 top-level directories
under /depot/mainline/, but only about 13 those need to be branched
for the beta.
    
I like the idea of branching mainline itself, just because it seems
easier to hold in my head.  What would it cost me to branch all the
other stuff too?  I think I remember reading that it doesn't cost
much until you touch the branched file.  Is that true?  Exactly
how much does it cost?  If I branch only subdirectories I think
we need to branch, how much will it cost me to label everything
else in case we want to branch it later too?

thanks, 
ab

- --
Adam B. Feder <ab at sgi.com>                  http://vrml.sgi.com
Cosmo VRML Engineering, Silicon Graphics    http://www.sgi.com/Products/cosmo