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Advantage of specify BLKSIZE=0 when allocat new dataset

 
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vijaykumar pande

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PostPosted: Thu Jul 19, 2007 12:43 pm    Post subject: Advantage of specify BLKSIZE=0 when allocat new dataset
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What advantage of specify BLKSIZE=0 when allocat newdataset
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sandeep1dimri

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PostPosted: Thu Jul 19, 2007 1:43 pm    Post subject:
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sandeep1dimri

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PostPosted: Thu Jul 19, 2007 3:03 pm    Post subject:
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Hi

It signifies the number of records in one block. And we provide BLKSIZE=0 means that we are not sure on the number of records in the block and so SMS takes care of BLKSIZE while allocating space for dataset. And it optimisze the number of records in one block.

So BLKSIZE=0 means optimize the number of records in one block.

Thanks
sandeep.
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vicky10001
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PostPosted: Thu Jul 19, 2007 3:07 pm    Post subject:
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How need to calculate BLKSIZE?

Example

LRECL = 800
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expat

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PostPosted: Thu Jul 19, 2007 5:00 pm    Post subject:
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vijaykumar pande
Quote:
What advantage of specify BLKSIZE=0 when allocat newdataset

BLKSIZE=0 can often cause problems if the dataset is not opened and closed unless your SMS environment has been correctly established.

If it has not, then the BLKSIZE=0 will be honoured and the dataset will have that attribute, which makes the dataset invalid for processing by DFHSM, or whatever other ILM software you use.

The correct coding is RECFM=xx,LRECL=nnn

vicky10001
Quote:
How need to calculate BLKSIZE?
Example
LRECL = 800

The calculation, should you wish to do it manually depends on the geometry of the DASD installed at your shop. The industry standard is currently 3390, which has an optimum BLKSIZE=27998.

This is great for VB files, RECFM=VB,LRECL=100,BLKSIZE=27998

For FB files, the formula is

INT(27998 / LRECL) * LRECL

But hey, why not let the system do it for you ..... it knows best icon_eek.gif
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Anuj Dhawan

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PostPosted: Thu Jul 19, 2007 7:27 pm    Post subject:
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Yup, this
Quote:
The correct coding is RECFM=xx,LRECL=nnn

is the best approach. Code this for your new dataset & let the system decide about BLKSIZE.

Expat,

I got a query here, I ran a test JOB:

Code:
//SORTIN   DD  DSN=HLQ.FIRST.FILE,             
//             DISP=SHR                         
//SORTOUT  DD  DSN=HLQ.FIRST.FILE.JUL19A,       
//             DISP=(NEW,CATLG,CATLG),         
//             DSORG=PS,                       
//             RECFM=FB,                       
//             DATACLAS=LARGE,                 
//             UNIT=SYSDA                       
//SORTWK01 DD  UNIT=SYSDA,SPACE=(CYL,(20,5))   
//SYSIN    DD  *                               
  SORT FIELDS=(1,3,CH,A)                       
/*                                             
//SORTMSG  DD  SYSOUT=*                         
//SYSOUT   DD  SYSOUT=*                         
//SYSPRINT DD  SYSOUT=*                         
//SYSUDUMP DD  SYSOUT=*                         
//CEEDUMP  DD  SYSOUT=*                         
//*                                             


First with BLKSIZE=0 & second time without BLKSIZE parameter. In both the cases I got Block size . . . . : 27920, why so? Does that mean, coding
BLKSIZE=0 & not coding it at all, are same?
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expat

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PostPosted: Thu Jul 19, 2007 7:59 pm    Post subject:
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It is almost the same, except that when the dataset is not opened then the BLKSIZE will equal 0.

If you use BLKSIZE=0 and the dataset is opened and closed by your program, it is the same as coding RECFM=xx,LRECL=nnn
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Anuj Dhawan

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PostPosted: Thu Jul 19, 2007 8:57 pm    Post subject:
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Thanks Expat, got it.
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