Re: RMAN questions...

"Brian Peasland" <dba_at_remove_spam.peasland.com> wrote in message news:3FB2B0AD.F839733D_at_remove_spam.peasland.com...
> > Because the *backup* takes less time. And less space.
>
> But you still need a baseline, or full backup.

Periodically, yes. But not every night. And that's the issue.

>That space is taken up no
> matter what.

Not necessarily as part of your 'immediate' backup space, though. You might push the full backup onto some tape unit, but keep the incrementals on a nearby server's hard disk, for example.

>And now I've got a full backup and an incremental backup as
> opposed to just one full backup. Since the space for any backup is
> greater than zero units, these mean a full and any incrementals takes
> more space than just a full. The presence/absence of archived redo logs
> does make a difference in this equation though.
>
> If taking less time to backup is a major factor then why do the
> incremental at all? Isn't that just wasting time? No incremental backup
> tonight means zero time spent doing the backup tonight. You still need a
> baseline which has to be taken at some time. Since you had to take the
> time to do the baseline, why not achieve savings of time by not doing
> the incrementals after that?

I know you don't mean that question seriously. It's a balance Brian, as you well know. If you take weekly full backups, and then do nothing, you will potentially have to apply a week's worth of archives when it comes time to recovering. So it's a balance between backup time and recovery time. Incrementals have a role to play in striking that balance.

I might well have a two hour maintenance window once a week, but a 20 minute window *during* the week. So I can do my full backups on Sunday, and incrementals during the rest of the week. Recovery time will be reduced because I will be able to recover a baseline from Sunday, update it with incrementals from throughout the week, and then only apply a little bit of redo at the end to bring it fully up-to-date (instead of restore Sunday's backup and apply all redo logs).

> I see your points. But I also see the *recovery* side of the coin too.

And you think I don't? I only mentioned backup times because your original post said, in effect, if using incrementals to *recover* is not faster, then what's the point of incrementals? Sounded like you *only* see the recovery side of the coin. The point I was making is that there's a balance between recovery and backup times, and incrementals help you strike that balance.

> After all, considering a backup strategy without considering the
> recovery strategy is to take the slippery slope.

When or where did I ever say anything that could be even remotely construed that way?

HJR Received on Wed Nov 12 2003 - 16:35:03 CST