Re: rman (again..and again..:-)

rogergorden_at_gmail.com wrote:
> Although it seems as if you don't need the archived files, (archived
> redo logs), you should always back these up because if the immediate
> backup of the datafiles is somehow corrupt, and you have to restore
> from an earlier backup, you will need these in order to properly
> recover your database. Without them, you can only do a partial
> database recovery and may only be able to open the database with
> missing data.
>
> Roger Gorden
> Senior DBA, Viewpoint Corp.
>

Oh dear, although I'm a bit late to the party, this particular gem I could not let pass.

Roger, your answer is full off the common misconception that people doing backups only want to restore to that point in time.

However, from the point of Oracles and most businesses view, people want to be able to survive a loss of file/filesystem/disk/machine with the least possible loss of data. And that is what archive logs give to you. Even if the loss of e.g. a datafile is days after the backup you're able to *recover* without any loss of data provided you're in archivelog mode _AND_ you still have all archived logs.

So archived logs not only cover corrupt backups (which they incidentally cover as a side effect) but only they allow you to get away after the loss of one or more datafiles.

You can't do a partial recovery, because under normal circumstances you're not able to open a database unless every datafile is recovered to the same point in time. What you're (hopefully) referring to is point in time recovery (PITR), but that's not partial recovery in my book - partial would mean you can restore then recover a single datafile to another point in time as the rest of the database. And that by definition is an inconsistent database, which in turn, won't open.

The only correct answer to anyone using archivelog mode is:

YES, you must backup archived logs using rman or OS methods as a means of protecting them, else why bother with archivelog mode in the first place?

And a final word to the OP: Who said that rman needs a database to be in archivelog mode for the backup? You won't be able to backup an open database, but it's not a prerequisite to use rman, however loosing most of it's advantages.

Cheers,
Holger Received on Mon Mar 14 2005 - 07:41:25 CST