Originally posted by jmodic
Note however that the entire block must be archived only when *the first* change to the block is made after the file has been put in a backup mode. Any further changes to that particular block will cause only vector changes to be recorded in archlogs, just as during the normal operation of the database.
It is not completely true:

During hot backup...
1. DBWR has written down the dirty block on a disk and this buffer in buffer cache has become free
2. Server process have read again this block from disk
3. Server process has made changes in the block and the block has become dirty again
4. Entire block must be archived again

P.S. Sorry for my bad english.