In Information center
http://publib.boulder.ibm.com/infoce...2%20%225%22%20
It says
RAID5 (with 4+1P) should be set to
DB2_PARALLEL_IO = *:4

And in best practices
http://www.ibm.com/developerworks/da...tabasestorage/
RAID 5 (4+1P)

db2set DB2_PARALLEL_IO=*,5



I am sure both cannot be true, I would say information center is correct. What do you guys think ?

On 21.10.11 16:07 , Kiran Hariharan wrote:
Correct.

Wrong. Syntax is wrong.

--
Helmut K. C. Tessarek
DB2 Performance and Development
IBM Toronto Lab

Is your answer above based solely on syntax, or are you saying that for
RAID-5 (4+1P) the correct value is *:4 rather than *:5 ?

On Sat, 22 Oct 2011 00:51:50 +0000, Mark A wrote:

Still waiting for a response. What is correct value (4 or 5) for 4+1P RIAD-5?

Don't worry about syntax or typos. If you don't know, please state that also.

Hi Mark,

Sorry, there are some weekends and days when I do not read the
newsgroup. Not answering was not on purpose.

On 10/25/2011 09:35 AM, Mark A wrote:
5 is the correct value. We are interested in the number of parallel IOs
we can do. I'm not sure why we are using a notation of 4+1P. If we use
RAID 5, one disk is always used as parity. But this disk is not
dedicated, which means we have 5 spindles which can do parallel IOs.

In my opinion we only need to know what kind of RAID and how many disks
there are in the array.

To put in in a nutshell: how many disks in the array can do parallel IOs?

WRT the documentation: I'll open a defect.

I don't want to be bitchy, but the syntax is quite important, if the
description of the problem is not detailed enough. If the OP had asked
the same question you did, then it would have been clear that the syntax
is not important.

P.S.: If I didn't know the answer, I would tell you.

--
Helmut K. C. Tessarek
DB2 Performance and Development
IBM Toronto Lab

On Tue, 25 Oct 2011 12:19:47 -0400, Helmut Tessarek wrote:
OP used 4+1P and said it was RAID-5. Yes that means 5 disks in each array (I am sure you are aware
that there can be as few as 3 and more than 5 disks in a RAID-5 array).

You can be bitchy if you want (doesn't bother me). This is a very confusing subject, which has
contradictory advice provided in several different IBM docs (and from different IBM employees), so I
was just wanting to make sure we got the right answer. It was not clear (to me at least) if you were
complaining about the 5 vs 4, or the syntax, which is why I asked. Any clarification of this subject from
IBM is certainly welcome.

On 25.10.11 15:12 , Mark A wrote:
Yep, I do. :-)

I have opened a documentation defect already. In some cases the documentation
is indeed confusing (in other cases even wrong) and I really ask anyone to use
the feedback link or post here in the forum.

In my first post I was complaining about the syntax and my answer was only
applying to the syntax (since I assumed the question was about the syntax).

In my second post I explained (hopefully sufficient enough) how to determine
the value to use.

As I said, it is only important how many parallel IOs are possible in your
RAID configuration. In the OP's example with a RAID5 (using 5 disks), the
number of possible parallel IOs is 5, therefore *:5.

--
Helmut K. C. Tessarek
DB2 Performance and Development
IBM Toronto Lab