Re: Current Redo got deleted

From: Don Seiler <don_at_seiler.us>
Date: Sun, 22 Mar 2015 20:34:42 -0500
Message-ID: <CAHJZqBB8qYOGD1v5gxTP4_vK3_idfb0KONu0BT6kvHrfaCfi7g_at_mail.gmail.com>

On Sun, Mar 22, 2015 at 8:27 PM, Mladen Gogala <dmarc-noreply_at_freelists.org> wrote:
>
> I beg to differ. There is no reason for redo log duplication if redo logs
> are already on RAID 1+0 volume, which they usually are. Redo log
> duplication in that case will force the database server CPU to do what the
> customer has already bought their SAN for. Your advice stands only if redo
> logs are on the local disks, which is exceedingly rare. The same goes for
> "normal redundancy" ASM disk groups. I see no reason for doing it, if ASM
> disk groups are on SAN, with built in redundancy., as is the case with RAID
> 1+0 LUNs.
>

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.

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

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Received on Mon Mar 23 2015 - 02:34:42 CET