Re: EMC RAID-5 and MultiPlexing Redo Logs

From: Howard J. Rogers <howardjr_at_www.com>
Date: Thu, 6 Sep 2001 06:12:03 +1000
Message-ID: <3b968614$1@news.iprimus.com.au>

By all means stick your data files on RAID5, but I wouldn't recommend your redo logs be placed anywhere near it. Redo logs are sequentially accessed, and constantly written to. RAID5 is bad news for both propositions (though whether the deterioration in performance will kill your database is something only you can work out.)

Even so, wherever you stick them, I would strongly urge multiplexing. That makes LGWR write twice (or, more sensibly, three times). The chances of LGWR throwing a wobbly and introducing corruption into the redo stream on one write is low, but not zero. The chances of it throwing the same wobbly in exactly the same place on the second and third writes is infinitessimally small. Net result: with raid-ed non-multiplexed redo, you are at some risk of unreadable redo. With raid-ed multiplexed redo, your risks are reduced hugely.

Regards
HJR "David Bye" <david_bye_at_bigpond.com> wrote in message news:_5nl7.28$c5.63_at_newsfeeds.bigpond.com...
> We are planning to deploy a 500GB database on EMC disks which are
protected
> by RAID-5.
>
> Is there any value in also using multiplexing ?
>
> Thanks
>
> David
>
>
>
Received on Wed Sep 05 2001 - 15:12:03 CDT