Question about remote TFile usage

Hi all,

I have a simple question:
TFile access is typically and in particular in connection with trees very efficient.
For example when reading only a branch out of a tree to first order only the data on disk that belong to the branch are read.

Now my question is: How much of this
efficient data access is kept when reading data remotely. For example comparing
rootd, dcache and castor access?
In case access to data is optimized
such that only as much as data is transferred as needed, then I assume the connection to the server delivering the data has to
be open at all times (via sockets?)
Or will there be reconnects if needed?

Thanks,
Constantin

-- 
Phone: +41-22-76 74875 (CERN)
Skype: loizides / AOL: ConLoi