tbmode/tbtape on Online 5

We need an "continuous" backup scheme that allows us to tell our users (in case of failure or disaster) up to what time the system can be restored So we came up with following scheme Use large logical log files ( a day's work ???) in combination with an hourly crontab job that has to do the following things 1) tbmode -l (lower L) to switch to the next logical log 2) tbtape -a to archive this last logical log to a) backup tape b) Unix file (on another disk) The following questions arise 1) what is the exit status of tbmode/tbstat (nothing in the manuals) (I assume 0 (zero) in the case of correct execution but what are the possible faults I have to watch out for ???) 2) do I have to move the Unix file inbetween tbtape -a's (or is there an append possible for backup of logical logs in Unix files ???) 3) suppose I drop the scheme and use smaller logical logs (an hour's work ???) combined with a continuous back up, can I still back these up to Unix file (does the second logical log backed up by continuous backup overwrite the first or will he be appended = does online close the logical log output device in between save's of logical logs ???) Any pointers on these matters would be very welcome