Re: Rman Explanation Please

artmerar@xxxxxxxxx wrote:
On Jul 31, 1:19 pm, joel garry <joel-ga...@xxxxxxxx> wrote:
On Jul 31, 8:42 am, artme...@xxxxxxxxx wrote:



On Jul 30, 6:02 pm, Palooka <nob...@xxxxxxxxxxx> wrote:
artme...@xxxxxxxxx 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
--
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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
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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
.

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