Re: Rman Explanation Please

From: Palooka <>
Date: Thu, 31 Jul 2008 21:07:34 +0100
Message-ID: <2Yokk.99746$8_2.84580@newsfe08.ams2> wrote:
> On Jul 31, 1:19 pm, joel garry <> wrote:

>> On Jul 31, 8:42 am, wrote:
>>> On Jul 30, 6:02 pm, Palooka <> wrote:
>>>> wrote:
>>>>> Hi,
>>>>> We just implemented RMAN and were reading the documentation and came
>>>>> across this:
>>>>> "For example, you can implement a three-level backup scheme so that a
>>>>> full or level 0 backup is taken monthly, a cumulative level 1 is taken
>>>>> weekly, and a differential level 1 is taken daily. In this scheme, you
>>>>> never have to apply more than a day's worth of redo for complete
>>>>> recovery."
>>>>> We;re trying to understand that.  The monthly level 0 is obviously a
>>>>> full database backup.  We do not understand the difference between the
>>>>> cumulative level 1 and the differential level 1 if both seem to use
>>>>> the monthly 0 as a source.
>>>>> How does that all fit into only needing 1 days worth of logs??
>>>>> Thanks all, we all appreciate it.
>>>> In principle, if you have your level 0 backup available, plus all your
>>>> incrementals, you can apply them all, and only need your logs since the
>>>> last incremental backup. But if it's the wrong day you might need to
>>>> restore 8 backups, plus apply today's redo.
>>>> Instictively I prefer cumulative incremental backups if it is feasible.
>>>> That way, you only need to restore one full backup, one cumulative
>>>> incremental, then apply archive logs since the last backup and the
>>>> online redo.
>>>> Palooka
>>> Palooka,
>>> So, you may suggest a weekly level 0 incremental backup, backs up the
>>> entire database.  Then after that, cumulative level 0 backups for the
>>> rest of the week.  Should a restore be needed, then restore the level
>>> 0 incremental, then the level 0 cumulative, then archive
>>> logs......correct?
>>> Seems simple enough....
>>> Thank you.
>> Um, doesn't the level 0 incremental have all blocks?
>> You probably meant to say cumulative level 1 daily.
>> The incremental stuff is a trade-off for places that have too many
>> changes to keep an incremental every day.
>> Not that I've ever tried it, just reading the docs.  I've enough
>> horsepower and disk to do a full every day.  Getting it offnode is
>> another issue, so I might start.  But that depends on management,
>> which is a more difficult problem.
>> jg
>> --
>> is bogus.  “The Court finds the memorial at Mt. Soledad,
>> including its Latin cross, communicates the primarily non-religious
>> messages of military service, death, and sacrifice.” - U.S. District
>> Judge Larry Burns, ruling that a giant cross on top of a hill is not a
>> religious symbol.
>> This needs a special black is white award.

> Jg,
> Here is what the docs say:
> Incremental backups can be either level 0 or level 1. A level 0
> incremental backup, which is the base for subsequent incremental
> backups, copies all blocks containing data, backing the datafile up
> into a backup set just as a full backup would. The only difference
> between a level 0 incremental backup and a full backup is that a full
> backup is never included in an incremental strategy.
> So, a level 0 is a full backup.
> In a cumulative level 1 backup, RMAN backs up all the blocks used
> since the most recent level 0 incremental backup. Cumulative
> incremental backups reduce the work needed for a restore by ensuring
> that you only need one incremental backup from any particular level.
> Cumulative backups require more space and time than differential
> backups, however, because they duplicate the work done by previous
> backups at the same level.
> So, that backs up all data since the lst level 0 incremental, or full
> backup....
> I mean, that is how I understand it........
Yes, a level 0 is to all intents and purposes a full backup.

The difference between a cumulative incremental and an ordinary incremental is that the former backs up all the changes since the last level 0, whereas the latter only backs up changes since the last incremental.

So time and performance permitting, I prefer the former, since if needing to restore and recover, I only need the last level zero, plus the last cumulative incremental (plus the redo of course), rather than ALL the incrementals since the last level zero.

Palooka Received on Thu Jul 31 2008 - 15:07:34 CDT

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