Re: disks for redo logs

From: joel garry <>
Date: Wed, 11 Feb 2009 11:26:37 -0800 (PST)
Message-ID: <>

On Feb 11, 7:40 am, helter skelter <> wrote:
> Hi,
> I've got two database - rac and single - and two RAID groups - 4 disks
> in RAID 10 and two disks in RAID 1 on storage array. At this time I'm
> using RAID 10 for RAC database redo and RAID 1 for single instance
> database redo.
> RAC is producing about 100% percent more redo then single db.
> I am wondering if it would be more efficiently to make one RAID 10 from
> 6 disks and use it for both database ? I have no possibilty to test
> this configuration so that is why I am asking You. Thanks for any advices.
> cheers

Impossible to tell. The bottleneck, if any, might be in the controllers or whatever. It doesn't really matter how much is produced, it matters what makes waits. While in general more spindles=better performance, your suggested amount of reconfiguration could easily be overcome by anything else. (and I would guess above) check out the ${ORACLE_SID} _lgwr*trc trace files, it spits out a message whenever log writes take more than .5 seconds or something, compare to your performance monitoring. I was a bit surprised when I first noticed what's in those traces, haven't quite figured out how to translate that for management. The surprising part was the size of writes versus the waits - apparently quite unrelated. Which I guess makes sense if the waits are caused by other things than the log writes.

I used to think having different volume groups would help, but I've been disabused of that notion. Now I don't understand it at all. SAN cache makes it all strange, too.

But hey, if users aren't complaining, everything is peachy. Right?


-- is bogus.
Received on Wed Feb 11 2009 - 13:26:37 CST

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