Re: Guaranteeing DB consistency with Split Mirror Online backups

Ian,
 Let me answer your question in two folds. First oracle 8i does have IO suspend features. ALter database suspend does that.

   Secondly the split mirror backup can be accomplished by issuing the alter tablespace begin backup command just before the split and the alter tablespace end backup just after. By doing this the file headers are frozen and splitting at that point gives a backup although not consistent. But while recovering if we have all the archive and online log files then the recovery can be made consistent.

HTH
Murali
"Ian Nash" <iannash_at_au1.ibm.com> wrote in message news:3bc3b5f4.0201302239.4115eb6f_at_posting.google.com...
> Hi,
>
> I am trying to understand how Oracle provides a guaranteed consistent
> database backup when using the "split-mirror" online backup approach.
> Because the "split-mirror" relies on the underlying hardware and/or
> software to manage, it is outside of Oracle's influence, and in
> particular, is relying on the Operating System to manage the
> consistency of the data in the filesystems in the mirrors.
> In AIX, there is no guarantee about data consistency (ie all blocks
> written and metadata consistent) unless the filesystem is unmounted.
> This is why it is recommended that a filesystem is unmounted when a
> mirror split takes place, as it ensures that all data blocks are
> written, and that no changes to data blocks are taking place as the
> split occurs.
> Hence, my question is how does Oracle (especially Oracle 8i which -
> AFAIK - does not have I/O suspend and resume features) guarantee a
> consistent and complete DB backup using the split-mirror online backup
> approach, when the underlying filesystem may not contain all written
> blocks if a split is taken with the filesystem mounted ?
> I have read the Oracle Whitepapers on this backup approach, and still
> cannot see how data integrity can be guaranteed for the data copy
> residing in the mirror.
> Ian Nash
> Adv(Thanks)ance
>
Received on Thu Jan 31 2002 - 07:29:28 CST