Shark configuration questions - not DBMS discussion

Richard Simpson

Shark configuration questions - not DBMS discussion
G'day,
My answer sort of depends on whether you have PAV or not. Its a
optional feature for SHARK.

If you have it, then in all circumstances (talking from a disk USAGE point
of view) you are better off with the largest disks you can get. After all
these volumes are fake anywhay and on the SHARK, especially with LLA, they
are really hard to hand tune in any meaningful way.

Without PAV you can only have one IO at a time in flight against an disk,
with PAV you can only have one in flight at any given time against 1
extent. That's a big difference. The amount of addresses you have is
constant, and PAV can always use them all, so the "larger" the disks you
have the more addresses you have spare for PAV and the less your IOSQ time
becomes (assuming you have the same number of extents as you did before).

If you have a SHARK 800, then you get 16 buckets (LCUs?) of 256 addresses.
If the SHARK is only sparsely populated then you might not be able to use
all 16 LCUs. You need to check how many you have available for the amount
of disk you are installing. Assuming you have PAV and plenty of addresses,
but few disks, then I would be tempted to stick with the model-3s. If you
are running low of addresses for any reason then upping the size of the
disk will relive this problem.

Here, I am trying to get "Large Volume Support" enabled and tested and
then move over to what I call "model 27s" but the manual calls something
like "custom sized" volumes.

One gotcha to be aware of is there is a 50K or so limit to the number of
tracks in a non Extended Format Non-VSAM file, which can limit how much of
a large volume a single dataset can use.

Incidentally, DFSMS, especially v1.3 (for ZOS) and beyond, has a lot of
nice features and works well witht he SHARK. Its well worth looking at.

Sorry for being a bit vauge about the exact terms. Once I finished the
SHARK project I was working on I recycled the nice redbook on the subject.


Regards

Richard Simpson
DB2 Performance Specialist
Systems Engineering & Architecture
IBM Global Services Australia
Cumberland Forest, FF12, (02) 9354 4220
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Steve Grimes

Re: Shark configuration questions
(in response to Richard Simpson)
Hello, Z/os 1.4, DB2 7.1 here,

Well, it looks like 8.5 Gb 3390-9's for us -- (unless a silver bullet
argument is waiting out there somewhere.) Here's the response I got (from
my e-mail that summarized the perspectives I got from IBM-Main and DB2-L.)
At least we won't be looking at 3390-3's!

>>Steve, Manuals on the Shark have more and more cautions as the disk size
increases,
>>including things like Large Volume Support is in system maintenance PTFs
and make
>>sure your ISV software supports volumes larger than 3390-9. These same
documents
>>say that 3390-9 volumes holding 8.6GB are supported without the cautions
- i.e. you don't
>>need PTFs and ISV software supports 3390-9s standardly.

>>Based on what I am seeing from the IBM publication side, 8.5GB volumes
seem a prudent choice.

>>While the documents are older than z/OS 1.4, it is possible that LVS
(Large Volume Support) is
>>integrated into the operating system. However, we run some ISV software
(like Cincom) that
>>is older and the cautions would still apply.

Thanks again for your inputs.

Stg

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