RE: Diff between "controlfile autobackup" and "snapshot controlfile"
- From: "Marquez, Chris" <CMarquez@xxxxxxxx>
- To: <iamanoracledba@xxxxxxxxx>, "Oracle L (E-mail)" <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 3 Feb 2005 14:50:04 -0500
Diff between "controlfile autobackup" and "snapshot controlfile"
All of my next comments are from the perspective that you are NOT using =
a RMAN Recovery Catalog database.
>>snapshot controlfile
>> There is no difference.
>> both produce a backup of controlfile
>> which can be used to recover database
This is a naive statement.
Every thing about RMAN and (backup/current) controlfiles has everything =
to do with "time" and "accessibility".
It's the classic "chicken-n-egg" scenario.
Only a valid controlfile that exists after the end of the RMAN backup =
("time")
*AND*
is available after the loss of all current controlfiles =
("accessibility")
has ANY USE!
You will note that the "snapshot controlfile" has date time stamp equal =
to the being of your RMAN backup session and is NOT subsequently =
updated.
As Jared pointed out it is used to freeze the controlfile at a point in =
time...a ""snapshot".
This implies that RMAN need consistent information for some internal =
processing?...don't know?
Since this "snapshot controlfile" is never updated it then knows nothing =
of the RMAN backup that has just completed and thus can not be used to =
restore the RMAN backup for which is was generated.
Simply, the "snapshot controlfile" is not for you, but for RMAN =
processing (might be useful for old backups).
So you move on to making your own "controlfile backups".
It critical to note that "controlfile backups" are needed for to =
reason's;
1.) You must have controlfiles for you database
2.) In the case of RMAN, the controlfile *IS* your backup data =
repository...Meta Data about previous backups before its creation.
All of my next comments are from the perspective that you have lost ALL =
live database controlfiles.
- "INCLUDE CURRENT CONTROLFILE"
I find this to be rather worthless. Simply because I have seen that =
this "controlfile backup" is wrapped up in the RMAN backup with the =
datafiles backup sets.
I can never pull it back unless I HAVE a (newer) controlfile the is =
*aware* of this backup...usless.
- "BACKUP CURRENT CONTROLFILE"
Don't like this one either, because you end up of with and RMAN binary =
backup version of your controlfile that I do not think is binary equal =
to a regular controlfile...so it must be restored...with a current =
controlfile!
- "CONFIGURE CONTROLFILE AUTOBACKUP"
I do not use this, but will look at my notes to see if I tested it.
This statement concerns me;
"a manually backed-up controlfile cannot be automatically restored."
This implies that a "CONTROLFILE AUTOBACKUP" can be automatically =
restored...but I disagree, about the usefulness of that..or the reality =
of that.
Again, using the RMAN rule (really all backup software rule), if I don't =
"Backup Meta Data", how can I restore anything!?
And if I do have a current controlfile ("Backup Meta Data") that can =
automatically restore my "CONTROLFILE AUTOBACKUP", that means the =
current controlfile is more current than the controlfile I will =
restore!...why do that?
The only way I see that CONTROLFILE AUTOBACKUPs might be useful is if it =
is a separate and identifiable RMAN file (set). Meaning I *might* be =
able to pick it out from a list of other RMAN backup files (sets. Then =
it can use it by RMAN to "replicate" or OS to "cp" it back as my =
database controlfile(s)).
Even still this controlfile backup would not be aware of subsequent =
archive log backups.
- "copy current controlfile"
Personally I like and use this it have never failed me to be able to =
restore after total loss.
I run this commend as the *final* command of my database, and archive =
log backups.
run {allocate channel c1 type disk; copy current controlfile to...
Effectively I'm backing up my "Backup Meta Data" at the end of each RMAN =
backup.
My RMAN shell scripts look like this;
backup archivelog all delete input... (logs between backups)
backup database...
backup archivelog all... (logs during backup)
copy current controlfile to...
I'm not saying do not use these other options, just be sure you know =
what your getting...what Restore & Recovery options with be available to =
you.
Simply, test, test, test, your backups!
You will know the true value of your controlfile backups if you blow =
away all the current one's
I was often fooled about my ability to restore until I was forced to =
restore ALL of my controlfile from my RMAN backups.
Backup is easy...it Restore & Recovery that hard!
hth
Chris Marquez
Oracle DBA
HEYMONitor=99 - heymonitor.com
"Oracle Monitoring & Alerting Solution"
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx on behalf of Sam Reddy
Sent: Wed 2/2/2005 4:25 PM
To: Oracle L (E-mail)
Cc:=09
Subject: Diff between "controlfile autobackup" and "snapshot =
controlfile"
Hi All,
What's the difference between "controlfile autobackup" and "snapshot =
controlfile" in RMAN configure ? Both are controlfile backups, what the =
difference between the controlfiles they backup ? Why there are two of =
these options ?
Thank you all
Sam
=20
=20
=09
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