Re: RMAN or Hot Backup
Date: Fri, 10 Apr 2009 11:36:25 -0700 (PDT)
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.
- More redo is generated. This can be an issue on a system that generates lots of redo to begin with.
- It becomes common for tablespaces to be left in hot backup mode, then people ask things like "why am I generating so much redo?"
- As Michael pointed out, suspend can be a problem on an unquiet system.
- 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.
> - 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.
-- _at_home.com is bogus. Mega Borg http://photos.orr.noaa.gov/gallery_4/incidents-34.htmReceived on Fri Apr 10 2009 - 13:36:25 CDT