Re: RMAN vs. OS Backups

From: John P. Higgins <jh33378_at_deere.com>
Date: Wed, 30 Dec 1998 21:14:06 -0600
Message-ID: <368AEBFD.EF98DEDA@deere.com>

We used to do OS backups, both hot and cold. The databases were small, and backup to the small, slow unix tapes was feasible. We had good scripts executed by cron. By good scripts, I mean that they automatically picked up the changes to the set of database files.

Then we installed SAP. The SAP databases are much bigger. We have over 30 databases in the 20 - 70 GB range. In the future, our databases may reach 500 - 1000 GB. 7*24 operation means cold backups are seldom possible.

We have been using OEBU (RMAN's predecessor) for 2 years. As we convert to Oracle 8, we are naturally converting to RMAN. We use Veritas NetBackup as our media manager. This routes the backups to a set of high-spead tape drives in a tape silo. Veritas keeps track of which file(s) are on which tape(s).

OEBU and RMAN error-checking is superior to anything we coded into our own scripts. It is not possible to get half a backup -- the backup job succeeds completely or it fails.

OEBU and RMAN automatically backup and purge the archived log files as part of every database backup. We also automatically run archive log backups / purges anytime the archive directory exceeds 50% full. This is where the network connection to the tape silo is a great benefit -- no one has to mount a tape.

We use two backup catalogs. One records half the databases, the other records the other half. Each records the backups of the other!

Don't belittle the benefits of the recovery catalog. This has all the info needed to recover a file, a tablespace, the whole system to current or a prior point-in-time. Yes, you could include all this in your OS backup scripts -- many (most?) do not.

As we have added databases, we have developed a procedure to restore a backup to a different machine and rename the database files, etc. In other words, we clone it. Easy with OEBU or RMAN -- a little harder with OS backups.

RMAN adds a new style of hot backup: it no longer must place a tablespace in backup mode before copying the files. This eliminates the increased logging that accompanies pre-RMAN hot backups.

Another new feature with RMAN is true, block-level incremental backups. We are still trying to optimize our strategy for incrementals.

As for export, we do a weekly export to /dev/null. This checks the validity of all databalocks below the tablespaces' high water marks. Since there is no possibility to recover logged transactions after an import, export / import has no place in backup / recovery.

I can't know your situation, so I can only offer our experience.

HTH

Rodgers, Tony (Atlanta) wrote:

Does anyone have any practical experience using RMAN in Oracle8
such that you could briefly explain the benefits of using it rather than
a
combination of O/S backups and exports?

I'm familiar with some of the benefits RMAN is supposed to offer in
general, but there is some overhead associated with its use (such as
the keeping of the recovery catalogs).  Is it simply easier to just do
operating system backups (cold) periodically than wrestle with the
RMAN configurations?  Or would you highly recommend using RMAN?

Just curious before launching a backup/recovery scheme for a
development database.

  Received on Wed Dec 30 1998 - 21:14:06 CST