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How many space is allocated?

 
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wanmkhk

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Joined: 04 Jul 2010
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Location: Australia

PostPosted: Thu Jul 22, 2010 7:17 pm    Post subject: How many space is allocated?
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//TEMP DD DSN=SYSXXX.XXXX.XXX.TEST,
// DISP=(NEW,CATLG,DELETE),
// UNIT=3390,
// SPACE=(CYL,(1,2),RLSE),VOL=(,,,3),
// DCB=(RECFM=FB,LRECL=80,DSORG=PS)

In this parameter "SPACE=(CYL,(1,2),RLSE),VOL=(,,,3)“, what is the possible maximum space allocation for this dataset TEMP?
1st allocation: 1 cyl
2nd allocation: 2cyl * 3 = 7cyl
3,4,.....16 is the same of 2nd allocation, ie 7cyl * 14 = 98 cyl
so, maximum space is 1 + 7 + 98 = 106 cyl.

Is it correct?
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Robert Sample

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PostPosted: Thu Jul 22, 2010 7:34 pm    Post subject:
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There is a link to manuals at the top of the page. You would do well to click on it and spend time reading the manuals. If you did so, you would find the JCL Language Reference manual, which says in section 12.68.2:
Quote:
Volume Count for Nonspecific Requests: If the request is for a nonspecific, public volume on a direct access device, the system ignores the volume count and allocates the number of volumes in the UNIT count subparameter.
So first, your VOL=(,,,3) is ignored.

Second, space allocation is per volume with a limit of 16 secondary extents per volume. So the first disk pack could have up to 1 + 2*15 = 31 cylinders of space.

Third, your unit count subparameter is 1 so multiple volumes will not be allocated.

Fourth, your math is completely wrong -- 7 cylinders would never be allocated for a secondary extent on this data set (only 2), even if there were multiple volumes allocated to it.

As an exercise, see if you can read the manuals and find out how space would be allocated on the second and third volumes (if you were using them) -- you might be surprised at the answer (hint: 7 is not it).
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expat

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PostPosted: Thu Jul 22, 2010 8:03 pm    Post subject:
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And also keep in mind that the allocation of a dataset extent may be satisfied by up to 5 physical extents.
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Robert Sample

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PostPosted: Thu Jul 22, 2010 8:06 pm    Post subject:
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I thought of mentioning that, expat, then saw the post had CYL=((1 so I decided the point was moot.
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expat

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PostPosted: Thu Jul 22, 2010 8:15 pm    Post subject:
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I only mentioned it because the secondary space request was higher than 1.

Anyway, I'm bored at the moment and for the want of anything better to do icon_lol.gif
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Pete Wilson

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PostPosted: Tue Jul 27, 2010 2:17 pm    Post subject:
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Suggest you include the 'Using Datasets' manual on your reading list. It's available on the IBM website.

This result of this space request would depend whether this dataset is SMS managed or not, and if the dataset was Extended Format or not (as defined by the datasets assigned Dataclas if applicable)

If it is non-SMS managed and being allocated on Public mounted volumes the rules Rob mentions above would apply.

If it is SMS managed the volume count is honoured, although the extra volumes will only be 'candidates' if they're not used (i.e. not enough data to need to write tto the 2nd or 3rd volume)

If Extended Format there can be up to 123 extents per volume.
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