Re: Which oracle server ?

From: Howard J. Rogers <hjr_at_dizwell.com>
Date: Mon, 13 Dec 2004 18:47:11 +1100
Message-ID: <41bd48f8$0$5112$afc38c87@news.optusnet.com.au>

Denis Do wrote:
> On 2004-12-13, Niall Litchfield <niall.litchfield_at_dial.pipex.com> wrote:
>

>>Howard used the word *may* and I
>>think that is exactly correct RAID 5 may be appropriate or it may not.
>>
>>

>
> Niall, but will it be correct from my side to tell, that
> in any case (even if usage of RAID5 is apropriate), its
> writing time wil be *much* slover than same hardware on 0+1?
>
> I think it is correct statement of mine :-), that is
> probably why alot of people advices against usage of RAID5
> as "carrier" for oracle FS.

Look: the arguments against RAID5 are generally well understood. They are also well expressed at www.baarf.com. I have read and recommended Cary Millsap's paper on that site to many. I would not ordinarily choose to implement RAID5. And of course there is a write-penalty with RAID5 over RAID0+1.

But the write penalty is not necessarily RAID5's main problem in these days of battery-backed cache -as Cary himself writes at one point, IIRC, so your statement that RAID 5 writes will be "much slower" than with RAID0+1 becomes extremely debateable. Like much else, it will depend.

Even so, the real problem with RAID5 is its performance under failure conditions. And under those same failure conditions, RAID0+1 would shine in comparison. No question, usually.

But RAID0+1 is a Gold Standard. It is expensive. And it's not the sort of thing you are typically going to implement with a Dell dual CPU box with just 3 hard disks. It is therefore (probably) inappropriate for the original poster, who has more major problems to deal with in any case (like the lack of a certified O/S and possibly low levels of RAM).

And unless you know something about the OP which I don't, then even the write penalty argument is moot. Neither you nor I know whether the original poster intends implementing an OLTP database, or a Data Warehouse, or something in-between. But *if* it was a Data Warehouse, which tends to be read-mostly, who cares about a write penalty?!

If you want to issue sweeping, generalised advice, that's fine, and I will happily join you in *generally* steering people away from RAID5, at least for their redo logs. But my comment that seems to have sparked this branch of the thread was an attempt to answer a *specific* question from a specific poster about a specific proposal. And generalised advice in those circumstances is not particularly appropriate, I think.

Regards
HJR Received on Mon Dec 13 2004 - 01:47:11 CST