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Question and Answer

Tom Kyte

Thanks for the question, Hien.

Asked: June 06, 2004 - 8:30 pm UTC

Last updated: July 09, 2004 - 7:10 pm UTC

Version: 10g

Viewed 1000+ times

You Asked

Hi Tom

Could you please explain why using RMAN for backup and recovery is more preferable than the user managed backup and recovery, including export and import.

I'd appreciate if you could illustrate the benefits of using 10g RMAN in a few bullet points.

Thanks in advance

Regards
Hien

and Tom said...

</code> http://docs.oracle.com/cd/B10501_01/server.920/a96566/rcmintro.htm#452952 <code>

I agree with all of those points. and as time goes on -- more and more reasons:

o RMAN checks blocks, you find corruptions at BACKUP time -- not at some point in the future. this is *key*

o RMAN can do true incrementals in 10g -- you have a 200gig database, change 500meg of it - RMAN will backup only 500meg, it will also read only 500meg (not 200gig)

o RMAN can do block level recovery -- you have a 16gig datafile, one bad block. RMAN can recover the block -- user managed recovery, the entire FILE. And the block level recovery is an online operation.

o 10g Disk based backup and recovery, fundementally changes the game.



do not even consider export and import "backup and recovery" tools. They cannot even compare to user managed recovery (they are point in time -- if done right. they are garbage otherwise (as far as recovery goes). they cannot be rolled forward at all)




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Comments

RMAN on the same box

Hien, June 16, 2004 - 2:04 am UTC

Tom

Thanks once again for your help.

Background:

We'll be running Oracle 10g on a small dual-process Sun SPARC 64 bit server. We have 2 databases and each has got 2 instances and we'd like to implement RMAN.

Questions:

Please let me know if it is not recommended, then is it safe to have RMAN repository on the same server with customer's databases. This is due to our Oracle CPU licensing restriction - or rather a budgetary constraint :)

Thanks
Hien

Tom Kyte
June 16, 2004 - 12:32 pm UTC

on a single machine how could 2 databases each have 2 instances (for 4 instances?)

and why would you run 2 databases on the same box, less bang for the buck there.

I would have a single database and just use rman to backup it up with the control file as the repository -- not big enough to warrant a repository, you don't have multiple (lots) of databases to manage.

Wrong Terminology

A reader, June 16, 2004 - 8:57 pm UTC

Tom

<QUOTE>
on a single machine how could 2 databases each have 2 instances (for 4
instances?)
</QUOTE>

It looks like that I still haven't got the terminology right, yet :)

It should be 2 applications 4 Oracle databases (ie 2 instances per application, TEST and PROD). Therefore there should be 4 instances on a single manchine (yeah, v. low spec too), TEST1, TEST2, PROD1, and PROD2. Wish me luck!

<QUOTE>
and why would you run 2 databases on the same box, less bang for the buck there.
</QUOTE>

Actually there'll be 4 databases for 2 applications (2 TEST's and 2 PROD's. We'd like to save on total licensing cost and hardware cost.

Regards
Hien

Tom Kyte
June 17, 2004 - 8:07 am UTC

you'll need more than luck.

there is an old saying, something about pennywise, pound foolish -- which only makes sense if you think in UK terms and their currency names....

You will be suffering performance issues. (you cannot manage 4 databases on a single machine, they are all independent, each can consume the machine)

You will have unplanned downtime as TEST kills your system.

You will waste more money by losing money due to this downtime, due to the extra work trying (in vain) to tune, due to the entire situation.



How does it know?

Christo Kutrovsky, July 09, 2004 - 6:28 pm UTC

<<<>>>
RMAN can do true incrementals in 10g -- you have a 200gig database, change
500meg of it - RMAN will backup only 500meg, it will also read only 500meg (not
200gig)
<<<>>>

How does RMAN know which 500 Mb have changed and reads only them? Is that on the file by file basis, or on the block basis? I hope you are not refering to archived redo log.



Tom Kyte
July 09, 2004 - 7:10 pm UTC

</code> http://docs.oracle.com/docs/cd/B13789_01/server.101/b10735/bkup.htm#1032144 <code>

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