RMAN – A Cumulative Incremental Backup Problem?

We were using a cumulative incremental backup strategy in Oracle version, patchset 21. We thought that each cumulative level 1 backup plus the level 0 which was taken prior to it, would be sufficient to restore the database. However, we found out while restoring the database to a DEV environment that this is not strictly the case…

For example, you have a level 0 backup from a Sunday night. Then on Monday, Tuesday and Wednesday you take cumulative level 1 backups. Now, you want to restore a copy of your database as of Wednesday night. You have been taking cumulative incremental backups each night, and have the level 0 also. So you take the level 0 from Sunday and the level 1 from Wednesday. This should be enough, you think?

Wrong. Sometimes, but not always, there will be files in the Monday and Tuesday night’s backupsets that are required in order to restore to the Wednesday level 1 point in time. Therefore, RMAN cannot remove the files from Monday or Tuesday until another level 0 has been taken (and depending upon your retention policy). This pretty much makes cumulative backups pointless, not to mention dangerous, so it might be worth using incremental differential backups instead.

This is just our experience, please let us know if this is not the case of I have got something wrong about cumulative incremental backups.

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Category: RMAN

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