Re: EMC RAID-5 and MultiPlexing Redo Logs

Howard J. Rogers wrote:
>
> 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
> >
> >
> >

And DON'T listen to those nice folks at EMC who tend to insist that:

• "Striping? Hell no, you don't that on our disks!"
• "RAID-5, RAID-S? That will run brilliantly on our disks!"
• "Sure they're really 20x18G disks, but our technology makes them seem like 40x9G"

blah blah blah blah

:-)

-- 
==============================
Connor McDonald

http://www.oracledba.co.uk

"Some days you're the pigeon, some days you're the statue..."