Hi




I know that nbackup keeps track of which blocks in the database changed and which did not so that backups contain only the blocks that changes since the last backup of the next lower level.
I want to use that feature to do syncs between servers.


I could simply create backups with incrementing levels, move the backup to the other server(s) and apply them there (that database is offline).
However, I suspect there is a limit for the number of backup levels a database can have.


Another strategy would be to lock the database, take a copy, unlock it and then use external software to do the diff.
However that would mean that the database would have to be copied very often and that a lot of extra space was needed.
That would mean a lot of disc io.


That could be reduced, if I locked the database, sync it using some software as rsync and then unlock it again.
I would not need extra copies any more, but a) the database would need to be offline much longer (remote sync needs more time) and b) it would have to be done for every replica again.




So here are my questions:


a) How many levels of backups can a database have (nbackup, not gbak)?


b) How bad is it (in terms of performance) to lock a database for a longer period of time?


c) Is there any way to get the information used by nbackup without actually creating a new backup level? (Just use this information to use external block copying?)


d) Is there any other good way to create a live exact replica?




Best regards,
Steffen