Re: RMAN or Hot Backup

From: Bob Jones <email_at_me.not>
Date: Fri, 10 Apr 2009 21:45:49 -0500
Message-ID: <yvTDl.23053$>

"Michael Austin" <> wrote in message news:fpSDl.26820$

> Bob Jones wrote:

>> "joel garry" <> wrote in message
>> On Apr 9, 5:07 pm, "Bob Jones" <em..._at_me.not> wrote:
>>> "jgar the jorrible" <> wrote in 
>>> On Mar 27, 5:15 pm, "Bob Jones" <em..._at_me.not> wrote:
>>>>> So yes, it is DBA basics. I really have not done too many Hot
>>>>> Backups, which is why I was asking what others opinions and experience
>>>>> with both are.
>>>> I have no idea why you guys keep referring to non-RMAN backup as "hot
>>>> backup". That is just wrong terminology.
>>> - We are referring to the copying of Oracle files while the db is
>>> - running. This results in an inconsistent set of data files, which can
>>> - be made consistent on recovery by the application of redo. However,
>>> - if the data files are not placed into backup mode before copying,
>>> - there may not be enough information in redo to make them consistent.
>>> - RMAN inconsistent backups are also hot backups, but RMAN is smarter
>>> - than operating system utilities and can copy the blocks in the data
>>> - files in a way that avoids the problems of redo, as well as avoiding
>>> - suspending the system.
>>> I am not sure what you meant by avoiding redo problems and suspending 
>>> the
>>> system. I see neither being a problem with non-RMAN backups.

>> - 1. More redo is generated. This can be an issue on a system that
>> - generates lots of redo to begin with.

>> Just make sure I hear this correctly. Non-RMAN backups cause more redo to
>> be generated?

>> - 2. It becomes common for tablespaces to be left in hot backup mode,
>> - then people ask things like "why am I generating so much redo?"

>> Still not understanding. Why would it generate more redo logs?

>> - 3. As Michael pointed out, suspend can be a problem on an unquiet
>> - system.

>> User-managed backups absolutely do not require system to be suspended. We
>> were doing backups long before RMAN even existed. Never once we had to
>> suspend the system.
> Bob, you miss understood this...  This is for a particular Storage Array 
> Vendor "copy" solution called a BCV (Business Continuity Volume) copy 
> where the database is put into hot-backup mode, alter system suspend, 
> split the "mirror", alter system resume, undo hot-backup mode.
> Having done these splits without the suspend mode you risk ORA-600s with 
> corrupted undo segments. Been there, done that.

Who said this is for your kind of backup in particular? We are talking about RMAN vs non-RMAN backup. Not using RMAN does not mean you have to suspend the system to do a backup. Received on Fri Apr 10 2009 - 21:45:49 CDT

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