Re: RMAN or Hot Backup
Date: Fri, 10 Apr 2009 20:21:19 -0500
"joel garry" <joel-garry_at_home.com> wrote in message
On Apr 9, 5:07 pm, "Bob Jones" <em..._at_me.not> wrote:
> "jgar the jorrible" <joel-ga..._at_home.com> 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
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
- 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