Re: Why is a backup of the controlfiles needed

From: Mark Bole <makbo_at_pacbell.net>
Date: Thu, 26 Aug 2004 17:00:08 GMT
Message-ID: <sGoXc.12509$JD5.7207@newssvr29.news.prodigy.com>

Rene Nyffenegger wrote:

> In article <IwnXc.12482$S35.9178_at_newssvr29.news.prodigy.com>, Mark Bole wrote:
>

>>Rene Nyffenegger wrote:
>>
>>
>>>In article <xfnXc.12475$1Y4.7457_at_newssvr29.news.prodigy.com>, Mark Bole wrote:
>>>
>>>
>>>>Albert Albani wrote:
>>>>
>>>>
>>>>
>>>>>I don't understand why backups of controlfiles are needed in an
>>>>>archivelog hotbackuped environment. The controlfiles should be multiplexed,
>>>>>so if one failes, there is always a good one around that can be copied.
>>>>>
>>>>>Is there a scenario in which a backup of a controlfile is truly needed?
>>>>>
>>>>>Thanks
>>>>>Albert
>>>>
>>>>They may be multiplexed, but they're still all on the same server. What 
>>>>if your server dies?
>>>

[...]
>
> I didn't mean to imply that backups of online redo logs should be taken.
>
> My point was: If I want to be able to recover until the very last executed
> commit, I need to make sure that I have access to at least one member
> of each group of the online redo log, no matter what happens to the
> server. If one hard disk crashes, bad, but not disasterous, because
> there is a copy of it on another harddisk. But if it is possible
> to get at least one copy of the online redo log, I can equally get
> one copy of a control file.
>
> However, your point is, as I understand it, if the server dies badly,
> you can at least make an incomplete recovery more easily because the
> control file had been backed up.
>
> Rene
>
>

Yes.

The only way I know of to guarantee zero committed data loss if your server crashes is to run Data Guard physical standby in maximum protection mode on another server (which introduces new costs and drawbacks).

This is somewhat OT from the original post but if someone is asking about why backups of control files, I think they should also understand the implications of all the other things that can and cannot be backed up, both on the same server and elsewhere.

As always, it boils down to:

• read the documentation
• search the net for additional discussions
• test, test, test

--Mark Bole Received on Thu Aug 26 2004 - 12:00:08 CDT