Re: QUESTION: Estimating required rman incremental backup size from redo??

On 25 Apr 2006 12:07:56 -0700, "BD" <bobby_dread_at_hotmail.com> wrote:

>Hey, all...
>
>I am in the process of capacity planning for an Oracle server
>(currently at 8.1.7.4, soon to go to 10g)
>
>We're in the process of rolling rman into our environments, but it has
>not yet gone to Production.
>
>A discussion started today as to how much space should be allocated for
>incremental backups, assuming we want to keep the most recent full,
>plus all subsequent incrementals, on the filesystem at all times.
>
>I can tell how much redo my Prod database generates for a certain day,
>but is there any correlation between that value, and the size that the
>same day's incremental rman backup is likely to be?

In my case before a certain database was migrated to a server on a 'corporate' site (and I lost control over backup, as the site didn't want to change their policies), the incremental was about the same size as the archived redologs.

Please also keep in mind, if you have incrementals, your archivelog backup is going to be ignored during restore and recovery. Also one can't use an incremental for block recovery.

>
>I started batting around the fact that redo contains pre-images of
>changed blocks as well as the change information, and also that it
>contains uncommitted transactions. So I would _think_ that rman
>incrementals (let's assume uncompressed for the moment) would be
>smaller in size than the same day's redo logs.
>
>I've seen threads in the group about this question - and in one
>response, the poster asked whether the OP intended to backup
>archivelogs as well (which I do), and that the relationship between
>redo volume and incremental backup size should be _created_ and not
>_discovered_ - but I'd really like to get an example from a functioning
>production environment.
>
>Ie "we have xxGB of redo on this day, and our compressed incremental
>rman backup from that day, including archivelogs, is xxGB".
>
>Would someone out there be able to provide a very quick example from a
>production environment? It would really help me in allocating disk
>space. ;-)
>
>Thanks!!
>
>BD

--
Sybrand Bakker, Senior Oracle DBA