Re: To use SAME or NOT for High End Storage Setup ?
- From: "Thomas Day" <tomday2@xxxxxxxxx>
- To: _oracle_L_list <oracle-l@xxxxxxxxxxxxx>
- Date: Mon, 15 May 2006 15:17:06 -0400
Jared has kindly pointed out to be that the first paragraph is less than
clear. I hope that I can clear it up without confusing myself further.
First, a few terms to define. This is from *Oracle(r) Database Performance
Tuning Guide, chapter 8 I/O Configuration and Design.*
"Stripe depth is the size of the stripe, sometimes called stripe unit."
"Stripe width is the product of the stripe depth and the number of drives in
the striped set."
"On low-concurrency ... systems, ensure that no single I/O visits the same
disk twice."
*My interpretation of this is that if you have few users then you want a
small stripe depth so that the I/O requests will be satisified with as many
disks as possible participating only once. The stripe width is not really
the issue. It may be large because of the number of drives participating in
the stripe set.*
**
"In a system with a high degree of concurrent small I/O requests, such as in
a traditional OLTP environment, it is beneficial to keep the stripe depth
large."
*My interpretation of this is that with many concurrent users you want a
large stripe depth so that a single I/O request can be statisified with just
one disk/head. This allows the possibility that other drives in the set can
satisfy I/O requests from other users.*
The SAME folks say to use a depth of 1M, regardless of the type of data
requests. See
http://www.oracle.com/technology/deploy/availability/pdf/oow2000_same.pdf
Their argument seems to be that for depths of under 1M the head seek time
starts to become a significant part of the response time. For depths of
over 1M the reduced amount of head seek time does not reduce the response
time significantly. I don't buy their argument completely but it's probably
good enough for the work-a-day DBA.
Other related posts:
