Oracle-L: RE: Do you use RMAN?

From: Reardon, Bruce (CALBBAY) <Bruce.Reardon_at_comalco.riotinto.com.au>
Date: Mon, 11 Mar 2002 20:28:19 -0800
Message-ID: <F001.0042526B.20020311202819@fatcity.com>

Pat & others,

For your information something that I hope is helpful.

To add a point we discovered the hard way - RMAN doesn't so much backup blocks containing data but rather it backs up blocks that have ever contained data.

To quote from Metalink note 105208.1:
"RMAN will not back up NEVER USED blocks, but will back up blocks that were used once, even if they are not in use now."

This can be a problem if you're not using uniform extent sizes and you temporarily get (say) large indexes.

In our case we worked around this at the time by rebuilding indexes to a new tablespace, resizing the original tablespace to a smaller value and then moving them back.

Our longer term "fix" has been to move to LMTs with uniform extent sizes.

Regards,
Bruce Reardon

-----Original Message-----
Sent: Friday, 8 March 2002 9:32

Bill ;

I am just in the process of implementing RMAN at our shop. We decided to go with RMAN for the following reasons :

Reason1 RMAN manages what backups are required to perform the restore and where the backup are located (will get the files off tape).
Reason 2 The ability to perform HOT backups without the "ALTER TABLESPACE ..BEGIN/END" commands. This will reduce the amount of REDO that is generated during the backup. IE: You get HOT backups with out the adverse impact of the volume of redo. Since a datafile does not have to be placed in backup mode - there is no risk of the database going down during a hot backup and asking for media recovery.
Reason 3 The ability to only backup "used" Oracle blocks. This greatly reduces the amount of data that needs to be backed up. BACKUP SETS - Will only copy database blocks containing data. This saves on IO by not copying empty blocks.
Reason 4 The ability to detect database block corruption. Because RMAN uses Server Processes to perform its backup reads - it will raise the same error a SQL statement will raise upon detection of something amiss inside a database block.
Reason 5 The ability to perform incremental backups and restores. This greatly reduces the amount of data that needs to be backed up (block level backups). LEVEL 0 - Will copy all database blocks containing data (FULL). This saves on IO by not copying empty blocks. LEVEL 1 - Will copy database blocks that have changed since the most recent level0 bkup. This further reduces IO. LEVEL 2 - Will copy database blocks that have changed since the most recent level1 bkup. This further reduces IO.
Reason 6 A Enterprise Centralized Backup and Recovery solution.

Patrick J. Howe
Oracle DBA
Illuminet Inc. (Carrier Division of Verisign) 4501 Intelco Loop SE
Olympia, WA 98507
Email : phowe_at_illuminet.com

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Author: Reardon, Bruce (CALBBAY)
  INET: Bruce.Reardon_at_comalco.riotinto.com.au

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Received on Mon Mar 11 2002 - 22:28:19 CST