Re: RMAN or Hot Backup

From: Bob Jones <email_at_me.not>
Date: Fri, 10 Apr 2009 20:21:19 -0500
Message-ID: <jgSDl.23051$>

"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.

  • 4. There are a bunch of salespeople running around selling systems
  • that propagate filesystems around, and too many people don't
  • understand why a disaster recovery based on the incorrect Oracle usage
  • will make a disaster, rather than recover from one.

Actually everybody knows that. Many just don't know enough about backups.

> - In this thread, and fairly commonly, the distinction is made by
> - calling the OS inconsistent copies hot backups and the RMAN
> - inconsistent copies RMAN backups.
> Actually this is the first time I have ever heard that.

  • Fair enough, usually called user-managed. I agree, there is too much
  • sloppy usage.

> - What terminology do you use?
> Anything but "hot backup". Not all OS backups are hot. They can be cold
> too.

  • Not really much advantage to cold backups, these days. Not using RMAN
  • these days can be categorized as "stupid, unless specifically
  • justified." And of course, RMAN can do cold too, as it has been able
  • to for a long time. Can't say as I've ever bothered with that.

Not using anything is stupid without justification including cold and non-RMAN backups. Received on Fri Apr 10 2009 - 20:21:19 CDT

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