We have done 300 GB restores.  The first thing I can tell you is that speed
has little to do with the amount of data and whole lot more to do with the
size of the files.  If you are talking about 1 large 400 GB DB file then it
will restore as fast as you tape drives can read it or as fast as your disk
drives can take it.  If it is millions of small files then throughput could
be dramatically reduced.  In our case we could restore one large file at
around 15 GB hour (from DLT tape).  When we had millions of small files it
would slow to .5 to 3 GB and hour.  The .5 was on restores where the average
file was 10 KB or less.  The 3 was on files where the average file size was
100 KB.  The issue is the Database reads required to restore millions of
small files.

Kyle
payne AT berbee DOT com