A reader, February 11, 2002 - 9:37 am UTC
can you specify some examples of RMAN features that we would lose if we use that strategy.
from the Backup class, it was mentioned that you could tell the catalog about any backups done outside RMAN. is this reliable and doable?
February 11, 2002 - 10:15 am UTC
For example -- incremental backups are not possible.
But -- the bottom line is -- you should have ALWAYS been doing hot backups. Split mirrors, unless you have triple mirroring, will open you up to failure during your backup and re-silvering window. Just do a plain old hot backup, its all you need or want. Don't over complicate the issue with split mirrors, re-silvering, datafile copies instead of RMAN backups and such.
Re-silvering
bob rich, February 11, 2002 - 10:51 am UTC
I am unfamiliar with the term re-silvering, could you explain?
February 11, 2002 - 3:06 pm UTC
It is the process of putting the mirrors back together -- "re-silvering" being a term borrowed from real mirrors we hang on walls and look at. You "re-silver" the mirror to sync it up with the copy.
Are Hot backups useful where nologging operations occur
Jim Dickson, February 13, 2002 - 4:25 am UTC
I have never fully understood the implication of taking hot backups only where the application performs most operations with nologging enabled.
Surely the lack of redo means there are some scenarios that cannot be fully recovered from OR that post-recovery there will be "soft corrupted" blocks.
My view is that the backup strategy is dependent on the application.
Oracle seems v sure in their recommendation that hot backups
are robust enough for all environments, so maybe i am missing something.
February 21, 2002 - 4:29 pm UTC
Hot backups and cold backups are not significantly different from each other in many respects. there are much FEWER options with cold then hot but they are very similar.
by the way -- it is really not HOT vs COLD, rather it is ARCHIVE LOG vs NO-ARCHIVE log. Whether you do hot or cold is up to you.
Lets take an example. We are in ARCHIVE LOG mode. I did a backup last night at 12am. At 8am this morning I did a non-recoverable action -- I did a create table as select without logging it and dropped the table I just copied (i did a "reorg" if you will). At 8:30am -- the disks that held the datafiles all failed. So, what can I do? I can restore my backup from lastnight and either:
o recover it to 7:59:59 AM (or any point in time between 12am and 7:59:59). I'll have my entire database back to what it looked like at that point in time. I'll have my table before I dropped it. We won't have the newly created table of course.
o recover it completely. Now I'll have all of my data EXCEPT that table since it was not logged.
in the real world, we would have backed up our datafile we did the create table as select without logging IMMEDIATELY after doing that operation to make it so we would NOT lose this data. We would tend to want to HOT BACKUP this file
Now, lets say we did the same thing in noarchive log mode. I did a backup last night at 12am. At 8am this morning I did a non-recoverable action -- I did a create table as select without logging it and dropped the table I just copied (i did a "reorg" if you will). At 8:30am -- the disks that held the datafiles all failed. So, what can I do?
o I can restore the database to 12am. Period, zippo, thats it, nothing else.
So, just to re-iterate -- it is not HOT vs COLD, its archive log vs no-archive log and you need to backup (probably in HOT mode) datafiles that are affected by non-logged operations ASAP after doing them to protect yourself. (eg: in my example above, I would have created the table as select, BACKED UP the affected file(s), dropped the old table. At no point in time would I have lost any data)
Data could be recoverd
Michael, February 16, 2002 - 12:44 pm UTC
Tom,
If I perform a online backup at 10am and I flush the redo log to archive log files at 10am and copy those file to tape at 10:30am, what time can I restore with those files on tape? 10am or 10:30am?
February 22, 2002 - 9:51 am UTC
10:30am.
you would restore the datafiles copied at 10am, apply the redo you copied at 10:30am.
Q on Backup
Anil Pant, December 10, 2003 - 12:35 am UTC
Hello,
I've couple of questions :
I've done a normal shutdown and all the datafiles are written, control files are updated and the DB is in consistent state. Now when I take a cold backup is it neccessary to backup the Redo Log files ? If yes then why do I require as everything is in consistent state and when I restart the DB it will start without reading the Redo logs as Im not doing any rollforward. Pls correct me if I've missed something.
December 10, 2003 - 3:03 am UTC
no, you do not need to backup redo.
if you do a hot backup (best, you should be doing those) you would not even CONSIDER backing up online redo.
if you do cold backups, you should shutdown cleanly (not abort) and you would not need to backup redo
if you shutdown abort, you would have to backup online redo logs as instance recovery would be mandatory. bad practice though.
can I recover logfile
Anurag, December 01, 2004 - 12:21 am UTC
Hi Tom,
A database is running in noarchive mode with 2 log groups(not mirrored), they take logical backups every evening, The current log is corrupted, and instance crashed (require instance recovery on next startup), Can I recover logfile. Help me How.
December 01, 2004 - 8:17 am UTC
contact support, your options are excessively limited. You were running your database in the mode that says "don't care what happens to the data, it is not important"
noarchivelog = YOU WILL LOSE SOME DATA SOME DAY
(not "might lose", it is most definitely "will lose" -- and today is probably that day)
"logical backups" are improperly named. they are "dumps of data from some prior point in time"
there is only one way to backup a database and export is not it.
noarchive
Anurag, December 01, 2004 - 11:17 pm UTC
Well, I agree with your point. Is there any way to recover , since data in a datafile is safe. only one can loose logfile contents since last checkpoint.
Shall I attempt to recreate logfile by recreating Control file through script in udump...incomplete recovery option. But what about instance recovery, since instance crashed.
Pls. Guide as contacting Support is the last option. I want to give my best try first.
regards
December 02, 2004 - 7:29 am UTC
how can you possibly say the data in the datafile is "safe"
it most certainly isn't - the online redo logs are what protect it.
you made the decision to not support media recovery (noarchive log)
and to have only one redo log (no multiplexing)
the only thing that means is "you are willing to goto your last full cold backup in the event of many trivial failures"
Sorry -- support is your FIRST OPTION <<<===== very very very first -- before you do something that precludes a partial recovery from happening. Now is not the time to be "guessing" and "trying".