Re: 2 recovery questions

Paul Murphy wrote:
> I've been reading about backup and recovery, but there are 2 questions that
> I haven't seen covered, but I'd like to know the answer to. If anyone would
> point me in the right direction on these, I'd appreciate it.
>
> 1. In Oracle 8i, do you really need periodic cold backups if you're running
> in archivelog mode or can you just use the hot backups of the data files,
> plus the archive logs from the time of the backup forward and the current
> control file and online redo logs to perform a recovery?
>

Depends what you're trying to accomplish with your backups. Traditional "cold" backups require a database shutdown for as long as it takes to copy your files, which, for many production systems, is an unacceptable loss of service. But they can be much easier for, say, a Windows or Unix sysadmin to restore in the middle of the night than hot backups .

> 2. From what I understand, if any copy of the control file is not available,
> the database will crash and you have to shutdown, replace the file with a
> good copy or remove reference to it from the init.ora and restart. Assuming
> this is true, I decide to only multiplex the online redo logs and archive
> redo logs on a remote server (because they can withstand a failure as long
> as one copy is available) and just multiplex the control file on multiple
> disks on the main server. I'm doing hot backups every night at 9PM, they
> finish at 11PM. The main server has a complete failure at 10AM the following
> morning. I restore the data files, control file, pre 9PM archive logs and
> init.ora from last night's tapes. I move the post 9PM archive logs and the
> online redo logs back from the remote server. The timestamps on the data
> files and control file are no later than11PM yesterday. Can I roll forward
> to point of failure (10AM the following day) with the post 9PM archive logs
> and use the undamaged version of the online redo logs copied from the remote
> server even though my control file's last timestamp was 11 PM?
>
> Thanks for clearing this up for me and anyone else who didn't know these
> answers.
> Paul Murphy
>

The best way to answer this question is to try it yourself (practice) in a test environment. Diaster recovery plans are next to useless if never tested.

If you have a hot backup and archived redo logs, you can also recover up through the time of the most recent archived log by creating a "backup controlfile" - examine the output of "alter database backup controlfile to trace" (in which case, unarchived redo log data is lost).

RMAN and DataGuard (standby database) are two Oracle tools you might want to become familiar with for alternatives to manual recovery.

--Mark Bole Received on Sat Jan 17 2004 - 12:24:34 CST