questions on the ff package

I wonder how efficiently it is to do the following command on a frequent basis.
nrow(matFF) <- nrow(matFF)+1

Obviously there is overhead (closing file, enlarging file, openeing file). 
I recommend you measure yourself whether this is acceptable for you.

no large file copying is needed each time the nrow is changed?

With a decent filesystem there is *no* copying from smaller to larger file.

would you think I can open 2000 large matrices and leave them open or I

need to close each after it is opened and used?

Not tested yet. 
I guess the number of open files can be configured when compiling your OS. 
Please test and let us know your experience.

Regards
Jens Oehlschl?gel