Re: RMAN or Hot Backup

From: Michael Austin <maustin_at_firstdbasource.com>
Date: Fri, 10 Apr 2009 20:30:38 -0500
Message-ID: <fpSDl.26820$yr3.4280_at_nlpi068.nbdc.sbc.com>

Bob Jones wrote:
> "joel garry" <joel-garry_at_home.com> wrote in message
> news:bd544f86-f3a8-4479-bc31-fb4cc5158675_at_i28g2000prd.googlegroups.com...
> On Apr 9, 5:07 pm, "Bob Jones" <em..._at_me.not> wrote:

>> "jgar the jorrible" <joel-ga..._at_home.com> wrote in 
>> messagenews:879adcc1-6bdc-493e-b003-301bc58ad40a_at_x31g2000prc.googlegroups.com...
>> 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