Re: Current Redo got deleted

From: Don Seiler <don_at_seiler.us>
Date: Sun, 22 Mar 2015 21:15:00 -0500
Message-ID: <CAHJZqBAkvoRVZzVqf-rD+4Ke4gPEVY03LWUOyz-V3GEEvwOPqg_at_mail.gmail.com>



Having duplexed redo logs in a different disk group would most definitely have given us a good shot at not having to fail over (and go through all the app server changes that is part of our internal process). The entire database is on that SAN and only one disk was affected. Granted having duplexed logs does incur a bit more log file sync waits, but that's the trade-off we've come to accept for now. Perhaps as we move to new storage hardware and the vendor can assure us beyond any doubt that we would be safe from such problems, we might consider changing. But it would take a lot for us to let our guard down now.

Yes we normally run with flashback on. The database is 28TB. Rebuilding it would have taken days compared to flashback and conversion which took about an hour. Any performance penalty from having flashback on is acceptable for us provided the benefits we have already seen from it.

Don.

On Sun, Mar 22, 2015 at 9:01 PM, Mladen Gogala <dmarc-noreply_at_freelists.org> wrote:

> On 03/22/2015 09:34 PM, Don Seiler wrote:
>
>> This sounds good in theory, but less than 2 months ago our SAN had what
>> can only be described as a "freak out" which resulted in the current
>> (non-multiplexed) redo log being corrupted. It forced us to failover to
>> standby (and then use flashback database to turn the original primary into
>> a new standby). The SAN disks were mirrored pairs and the redo disk group
>> was external redundancy, FYI. We're entertaining new storage vendors that
>> also insist that we don't need to multiplex redo logs with their magic RAID
>> sauce but once bitten, twice shy, as they say. I can't in good conscience
>> leave us exposed to that vulnerability again.
>>
> Don, what would have changed if the redo logs were duplexed? Where would
> you dupliex them to? Another SAN? If SAN freaked out (your expression, not
> quite sure what does it mean) and the duplexed redo logs were on the same
> SAN, what would that duplex copy do for you? Yes, that's the case for
> fail-over to standby. What protected you in this case was a standby
> database, not duplex redo logs. I don't see that anything would be
> different if you had another set of redo log files on the SAN that has
> "freaked out". I am a big fan of standby databases, especially active DG
> which can also be used as a reporting server.
> I also have a question: do you normally run your production databases with
> the flashback on? The cost of that can be quite severe. I would have
> rebuilt the primary from backup.
>
>
> --
> Mladen Gogala
> Oracle DBA
> http://mgogala.freehostia.com
>
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>

-- 
Don Seiler
http://www.seiler.us

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Received on Mon Mar 23 2015 - 03:15:00 CET

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