Hi Mark, Yes I am thinking about the O/S block writes. If I understand you correctly, you're saying that since DBWR schedules these as packaged O/S writes they are likely to either succeed or fail in their entirety and unlikely to lead to split blocks - although that could happen under some circumstances. So very occassionally you may indeed see a server requiring media recovery following a crash. The difference with backups is that a crash is fairly instantaneous so you've only got a tiny window in which the split block will possibly occur - so it's rare. During backups the file copying/writing mechanism runs scanning files for a long time while DBWR is potentially busy - so there's a much bigger window for it to pick up a split block - hence it's not so rare and the need for BEGIN/END BACKUP to accommodate this. Have I got it now?! Thanks for your help Charlotte > I think the questioner is asking about the 512 byte components of the write >of the Oracle block. > >In a non-RMAN backup, the operating system utilities have no particular >interest by default in copying chunks (n of the usually 512 byte pieces) in >anything like an >alignment matching Oracle's blocks. DBWR, on the other hand, will definitely >submit Oracle blocks as integral sets of the pieces that make up the Oracle >blocks from the underlying OS pieces. > >So the risk goes way, way down. I'd quibble slightly with Tanel's "always" >remark. If you restart and it tells you media recovery is required, then a >file really did get crashed and one of the cases of >a file getting trashed is that it is not marked fuzzy and a block's header >and tail don't match. Then you would have to get a previous backup of the >file (or block) and roll it forward. So the recovery is just the same as if >you lose a file for any other reason. When I've gotten a file trashed >(...never on a client of mine with at least duplex plex images, but >frequently in the dim past when lots of folks used single plex images) I >never saw a block that looked complete except for a mismatch, so I'm >thinking this is very rare. > >Regards, > >mwf __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com -- //www.freelists.org/webpage/oracle-l