hi again,
A few more from my notes about COLD v/s HOT backups!
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Why would you be doing cold backups at all???
You do not want to do the split mirrors. You will obviate many of the benefits
and features of RMAN. You should just be doing HOT backups with RMAN (no need
to "alter tablespace begin/end backup" with RMAN).
You can do the split mirrors with RMAN but its just like doing the backup
without RMAN. You will lose the features available in RMAN that aren't
available without RMAN.
Just do hot backups right now. They are not any harder then cold backups. Your
system should be 100% available right now, today, nothing special need be done.
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.
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)
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Hope this helps!
Best Regards
Yogeeraj
No person was ever honoured for what he received. Honour has been the reward for what he gave (clavin coolidge)
