Re: RMAN or Hot Backup

From: Michael Austin <>
Date: Fri, 10 Apr 2009 20:30:38 -0500
Message-ID: <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. Received on Fri Apr 10 2009 - 20:30:38 CDT

Original text of this message