Re: Backup strategy using RMAN

On Wed, 18 Sep 2002 15:51:42 +0200, Candido Dessanti <termy_at_blunet.it> wrote:

>
>> The "fact" that incremental backup take the same time as a full backup
>> is kinda new to me.....true that RMAN must check all blocks in the DB
>> in both cases, but there is definetely a difference between finding
>> 90% and 2%of the blocks changed......from where does this "fact" come
>> ?
>
>With oracle8 is definetly the same for me...what is a backup if not
>reading blocks from database?
>And incremental has to read all datafiles blocks, so the time would be
>the same, or at least is the same on small sized database using solaris
>6 and oracle 8.0.6
>I
>
>

I still do not understand. Example :

You have a database with say 1,000,000 blocks

 A full backup would require 1,000,000 blocks to be read AND to be written to the backup media. This writing takes time, right ?

An incremental backup will also read 1,000,000 blocks and write <= 1,000,000 blocks, depending on how many blocks have changed since the last backup.

So the incremental backup will, everything else being equal, always take less time than the full backup since it will *at most* need to write 1,000,000 blocks.

In the case of only 2% of the blocks having changed since the last backup, the writing time will only be 2% of the full backup => incremental backup would be *much* quicker than full backup.

Or what ?

• Kenneth Koenraadt