RE: stipe size

Watch out, though. If you set the stripe size to *only* the value of the max atomic I/O size, you've got to make sure that your logical and physical stripes are aligned. (See Hank Tullis's article at hotsos.com.) Otherwise, you'll end up having a single I/O call split into two simply because there'll be a physical boundary in the midst of a logical stripe.

Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
* Nullius in verba *

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-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Mladen Gogala Sent: Wednesday, February 25, 2004 11:00 PM To: oracle-l_at_freelists.org
Subject: Re: stipe size

On 02/25/2004 11:31:35 PM, Cary Millsap wrote:

> What is "small"? I think anything less than about 1MB is small, even
for
> TP. Since 7.3, the Oracle kernel does its very best to do large read
> calls. This is a Good Thing. Using stripe sizes that cut a single
large
> I/O call into multiple parts is a Bad Thing on a many-user system.

Well, here's the problem: Unix system can do atomic I/O as large as the maximum size of it's kio buffer (kernel I/O buffer). On most systems, kernel I/O buffer max size is between 256k (Solaris 7) and 1M (HP-UX 11, 64 bit). If the stripe size is larger then that, OS will need 2 or more I/O requests to read a single stripe. That is the same reasoning as behind not setting DB_FILE_MULTIBLOCK_READ_COUNT

too high. So, to be on the safe side, I'd find out the max size of the atomic I/O and set stripe size to that value. I think that 256k is just about ideal. Of course, there is an additional element of RAID on board cache which is really the element that communicates with the server. If cache is big, then you want big prefetch, to speed up subsequent I/O requests. In that case, it's "the bigger, the better" thing with stripe size.

>
> <what-would-Mladen-do>
> ...However, if the original question is really about "stipe size," I
> believe that Michael Stipe is a little bitty devil, probably not more
> than about 5'4" at most. But this is really outside of my subject of
> expertise.
> </what-would-Mladen-do>

Actually, "Stipe" is a name in my country of origin (Croatia). It is a derivative of "Stephen" and funny thing is that the current president of Croatia is a guy named "Stipe Mesic". Not being a great admirer of Mr. Mesic, I find the thread about his size hilarious. Of course, the common wisdom is that size doesn't matter, but..., but I've definitely gone off topic with this.

-- 
Mladen Gogala
Oracle DBA
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