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Tom - I am trying to figure out a cheap.. *nearly* 24x7 solution which has me a little confounded. $$$ is an issue. I am aware of the usual redundant options, parallel server, fail-over, stand-by etc., However, since $$$ is *such* an issue for reasons I won't get into, I have the following choice:
Hot backups only.. no redundancy in hardware etc.,
Investment in Shark Drives which will allow for a cold backup with only 15 min. of down time per day..
The question is the following.. Of all the seasoned Oracle DBA's I know, none really cares for hot backups although perhaps I am too green to know why. They say they are complicated, tricky, sometimes unreliable etc., Q1 is, can you confirm or deny this? Is it a matter of just really knowing what you're doing? If so, how can I ensure I really know what I'm doing.
If an investment in amazing disk drives would allow for a cold backup instead of a hot one, which would you pick and why? The more expensive option which is preferred by many of the crew is dual-ported disk drives across two boxes (parallel server).. however, I'm afraid this is too much $$$ once again.
Thanks,
Doug
PS Love your book..
and Tom said...
Funny, out of all of the seasoned DBAs I know -- hot backups are the ONLY WAY TO GO.
If they feel otherwise, I would quite simply LOVE to hear why.
Using RMAN, there is NO difference between hot and cold.
Using tar/cp/whatever, you must put a tablespace into backup mode but other then that, THERE IS NO DIFFERENCE between hot and cold (mechanically speaking).
Now, a cold backup does have the somewhat bad side effect of wiping out your shared pool, your buffer cache and preventing your users from logging in to do work. Your database is like a car, it runs better when it is warmed up. If you want to cold start it - be prepared for rough running when you restart as we have to rebuild that shared pool, that buffer cache and so on.
I would say you do not know seasoned DBAs, you know people who haven't had the real experience, who don't know any better, who are able to get away with shutting down the database by keeping those "who don't know" in the dark.
The only kind of backup we do on our production systems here is hot, I'd say we have more then one or two seasoned Oracle DBA's.
Hot is no harder (or easier) then cold. You need to retain the same exact amount of archived redo log and so on (i truly hope that they run the production databases in ARCHIVELOG mode, else I can assure you that you will lose data someday).
Hot is not unreliable, it is something we sort of pride ourselves on -- being able to recover from failure (it is after all, one of the major reasons you are using a database).
I can most wholeheartedly DENY their unfounded misconceptions and if one of them would care to discuss it, I'd be more then willing to open a special thread on it.
It is, like everything else, a matter of knowing what you are doing. To ensure you know what you are doing, get a test system and practice. Put the database into archive log mode, do your hot backups to another disk, bang on the system and then do things like:
o disconnect the drives with the system tablespace and recover.
o wipe out all of your control files, and recover
o wipe out an online redo log group while its active and recover as much as you can
and so on. practice, testing, simulation. thats the only way.
I would never pick cold over hot given the chance. No benefit, only downsides.
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