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Space parameter and resulting allocation different.

 
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John Young

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PostPosted: Tue Feb 07, 2012 12:53 am    Post subject: Space parameter and resulting allocation different.
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I have been trying to allocate a VSAM data set of an exact size, with 10 cylinders primary, and 5 cylinders secondary.

The resulting allocation (from LISTCAT) indicates primary of 23 cylinders and a secondary of 12 cylinders.

The data set IS SMS managed.

It appears SMS is making a decision to increase the allocation. Can the allocation be influenced to make it the specified size?
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Robert Sample

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PostPosted: Tue Feb 07, 2012 1:05 am    Post subject:
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Discuss the problem with your site support group. SMS policies can override JCL allocations, and it may -- or may not (depending upon the site -- be possible to change the actual allocation.
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Bill Woodger

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PostPosted: Tue Feb 07, 2012 1:10 am    Post subject: Reply to: Space parameter and resulting allocation different
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You could also consider this recent topic.
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enrico-sorichetti

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PostPosted: Tue Feb 07, 2012 1:33 am    Post subject: Reply to: Space parameter and resulting allocation different
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VSAM extent consolidation has struck again ...

from some IBM pubblication ...
Quote:
Extent consolidation
z/OS consolidates adjacent extents for VSAM SMS managed data sets when extending on the same volume. VSAM extent consolidation is automatic and requires no action on your part. If the extents are adjacent, the new extent is incorporated into the previous extent. This means that first extent tracks as seen on ISPF 3.4 Data set level listing shows allocations larger than the primary when extents are adjacent to the primary (Figure 7 on page 13 and Figure 8 on page 14).


IIRC since zOS 1.5

here is a link to the official IBM manual
z/OS V1R11 DFSMS Using Data Sets
http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/DGT2D480/CCONTENTS?SHELF=DGT2BK91&DN=SC26-7410-09&DT=20090522090215
and the exact page
http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/dgt2d480/2.2.2.4.6?ACTION=MATCHES&REQUEST=consolidation&TYPE=FUZZY&SHELF=DGT2BK91&DT=20090522090215&CASE=&searchTopic=TOPIC&searchText=TEXT&searchIndex=INDEX&rank=RANK&ScrollTOP=FIRSTHIT#FIRSTHIT
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John Young

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PostPosted: Tue Feb 07, 2012 1:40 am    Post subject: Space parameter and resulting allocation different.
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Yes, I saw the information about extent consolidation, but the difference in the specified space, and the actual allocation are before any data has been loaded into the file.

Our ACS routines do not make any changes to the allocation parameters.
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enrico-sorichetti

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PostPosted: Tue Feb 07, 2012 1:43 am    Post subject: Reply to: Space parameter and resulting allocation different
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hard to believe... IT is pretty deterministic
and software is usually pretty dumb, it does only what it is told to do icon_cool.gif
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vasanthz

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PostPosted: Tue Feb 07, 2012 12:03 pm    Post subject:
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Hi,

Quote:
with 10 cylinders primary, and 5 cylinders secondary.
The resulting allocation (from LISTCAT) indicates primary of 23 cylinders and a secondary of 12 cylinders.

Maybe you are specifying the space in 3380 device and SMS allocation exit is configured to allocate in 3350 device type.

In this case,
5 cylinders on JCL would result in 12 cylinders allocated.
10 cylinders on JCL would result in 24 cylinders allocated.

math:
5 cylinders * 15 = 75 tracks.
3380 track size * number of tracks = 47476 * 75 = 3,560,700 (total size)
round down(Total size / 3350 track size) = round down(3560700/19069) = 186 tracks.
round down(186 tracks / no of tracks per cylinder) = round down(186 / 15) = 12 cylinders allocated.

Similarly,
10 cylinders * 15 = 150 tracks.
3380 track size * number of tracks = 47476 * 150 = 7121400 (total size)
round down(Total size / 3350 track size) = round down(7121400/19069) = 373 tracks.
round down(373 tracks / no of tracks per cylinder) = round down(373 / 15) = 24 cylinders allocated.

Disclaimer: I myself don't trust my math. Verification of above is recommended.
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enrico-sorichetti

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PostPosted: Tue Feb 07, 2012 2:05 pm    Post subject: Reply to: Space parameter and resulting allocation different
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nice shot Vasanthz
anyway it is not an allocation exit, it is the standard SMS logic flow
http://publib.boulder.ibm.com/infocenter/zos/v1r12/index.jsp?topic=%2Fcom.ibm.zos.r12.idas200%2Fs2057.htm

the default device geometry is the first thing to set when defining a NEW sms configuration
wonder why they fouled up such a simple parameter
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Pete Wilson

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PostPosted: Wed Mar 21, 2012 3:22 pm    Post subject:
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The CI and CA freespace values can affect the allocation size significantly. What have you specified for this file?

When you say it has become 23cyls is that immediately after defining the cluster or has it been loaded wih data?

Check the Dataclas assigned to the file as well, it may have overriding space values set. You can check the Dataclas values in ISMF option 4
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