June 07, 2007

RMAN vs OS backup on NetApp

Before RMAN emerged, OS backup is the main way to backup a database. It has shortcomings:
  • Cannot do incremental backup. If datafiles are big, the backup time is long
  • It takes more disk space
  • You cannot really know whether your backup will come to rescue in disaster. RMNA offer the ability to validate the backup

RMAN offers the following bonous beyond the normal backup

  • RMAN can compress the backup
  • RMAN can check the corrupted data block during backup.
  • RMAN can delete obsolete backup set

One shortcoming of RMAN is that you have to maintain a repository server to make full use of RMAN.

The pendulum has swayed so far in favour to RMAN that OS backup seems to be dead.

NetApp’s Snapshot change the balance a bit, if not completed reverse the trend.

With Snapshot,
  • the backup time is long. The backup process almost take no tiime and the size of DB is irrelevant. I now take backup every hour.
  • It takes more disk space Snapshot do incremental backup at OS level.
  • RMAN can compress backup With OS level incremental backup, this is not important
  • MAN can check the corrupted data block during backup Still an advantage
  • _RMAN can delete obsolete backup set Snapshots can be deleted by a scripts
Tremendous advantages of Sanpshot are:
  • The backup is superfast
  • Restore is easy. Just normal OS copy. It should be a little faster than RMAN restore since RMAN need to restore the backupsets to OS files.
  • Get rid of repository server.

I have not got a chance to test “SnapManager for Oracle”, which combine Snapshot with RMAN. Maybe after I do that, I will have different opinion.
So far, Snapshot + OS backup will supersede RMAN.


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