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optimum BLOCK SIZE (BLKSIZE)

 
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dharmendra_kp

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Joined: 10 Mar 2005
Posts: 33
Location: Lewiston

PostPosted: Fri Feb 09, 2007 8:10 pm    Post subject: optimum BLOCK SIZE (BLKSIZE)
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Hi all,
how do you calculate optimum block size for a given LRECL? This parameter plays an important role for an input or output file for production environment.

Please share the knowledge with the forum.

Thanks & Regards.
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William Thompson

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Joined: 18 Nov 2006
Posts: 3158
Location: Tucson AZ

PostPosted: Fri Feb 09, 2007 8:24 pm    Post subject:
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Find the largest blksize that one or two blocks will fit on a track and is a multiple of the record size.
Or lst the system take of it for you with a blksize=0 (SDB i think?)
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UmeySan

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Joined: 22 Aug 2006
Posts: 757
Location: Germany

PostPosted: Fri Feb 09, 2007 8:24 pm    Post subject:
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Hi !

First of all it depends of the modell-numer of your installed disks.

Try TSO 3.2 and enter the attibutes of your desired file without
BLKSIZE. Press enter. Then have a look at at the cataloged file for
the blksize. Use this size in your jcl.

Regards, UmeySan
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dick scherrer

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Joined: 23 Nov 2006
Posts: 19270
Location: Inside the Matrix

PostPosted: Fri Feb 09, 2007 10:09 pm    Post subject:
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Hello,

Also, you can specify BLKSIZE=0 in your jcl and most sites generate an appropriate blkzise.
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mmwife

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Joined: 30 May 2003
Posts: 1592

PostPosted: Sat Feb 10, 2007 4:54 am    Post subject:
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If full SMS is active in your shop you don't have to specify a blksize.

It's best to let the sys do it (SMS or blksize=0) because when there's a DASD conversion at your shop the next file created w/the JCL will posess an optimum blksize for that device type.
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