1st extent cylinders

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1st extent cylinders

Postby GeorgeQ » Wed Aug 16, 2017 1:05 am

Hello everyone,

I try to allocate new dataset with different space,
every time the dataset I allocated show me 1st extent cylinders is 1.

for example: SPACE=(cyl,(10000,6000)). ---(in this example I think 1st extent cylinders should be 10000)

I changed this to different value but each time the value of 1st extent cylinders is still 1.

May I ask what the 1st extent cylinders mean? how to change it?

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Re: 1st extent cylinders

Postby Robert Sample » Wed Aug 16, 2017 1:22 am

First, unless you use DSNTYPE=LARGE in your JCL for the DD statement, you are limited to 4369 cylinders per volume. So trying SPACE=(CYL,(10000,6000)) won't work without a DSNTYPE=LARGE parameter on your DD statement.

Second, your site can establish rules for data set allocations under SMS control. And those rules can override whatever you put in your JCL.

You need to talk to your site support group to find out what the allocation rules are for data sets and what you need to do to allocate data sets larger than 1 cylinder. Nobody on this forum works at your site, so we have no idea how your site coded its SMS rules and therefore how space allocation will work. We can tell you how it would work if you're not under SMS rules, but that doesn't help you. Contact your site support group.

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Re: 1st extent cylinders

Postby steve-myers » Wed Aug 16, 2017 8:30 am

GeorgeQ wrote:... May I ask what the 1st extent cylinders mean? ...

The ISPF panel words it that way for a reason. When your JCL specifies something like SPACE=(CYL,(50,10)) the initial allocation of 50 cylinders can be split into as many as 5 real extents. So the real space can be allocated as 46 cylinders and 4 additional cylinders. It could even be 1, 1, 1, 1, 46. So ISPF is reporting what it sees. The initial allocation amount specified in your JCL has been discarded; ISPF cannot recover it.

This topic is discussed in more detail in SPACE parameter topic in MVS JCL Reference for your z/OS release.
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