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girish.kanswa
Warnings : 1
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Joined: 13 Nov 2007
Posts: 2
Location: pune
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Hi All,
Can you please tell me what is the significance of blksize in JCL..?
Thanks in advance |
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References
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 Splitted: Wed Jul 09, 2008 5:28 pm by superk From Topic can we pass numeric value in PARM (IMS DB/DC) |
expat
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Joined: 14 Mar 2007
Posts: 3507
Location: Brussels once more ...
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| I generally do not specify it, just let the O/S do the work for you as it will select the best BLKSIZE for the output device being used. |
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Anuj D.
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Joined: 22 Apr 2006
Posts: 2156
Location: Phoenix, AZ
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Bill Dennis
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Joined: 17 Aug 2007
Posts: 311
Location: Iowa, USA
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| Combining small records into blocks make I/O and data storage much more efficient and can reduce elapsed time to run a job. A file's BLKSIZE can be specified in a program but the best practice is to allow the JCL or system to set it. Most times you can specify BLKSIZE=0 and the system determines the best blocksize for the device. |
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dick scherrer
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Joined: 23 Nov 2006
Posts: 8638
Location: 221 B Baker St
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Hello,
| Quote: |
| Can you please tell me what is the significance of blksize in JCL..? |
The main significance of the block size is the difference between physical and logical input/output actions. Basically, if your data has one record per block, every single read or write requires physical i/o. If your data has 1000 records per block, the number of physical reads or writes for 1000 records is one.
Another very important consideration the block size determines is how efficiently your data is allocated on the media (dasd more so than cart/tape). Efficient block sizes can greatly reduce the amount of media needed to store the data. |
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expat
Global Moderator
Joined: 14 Mar 2007
Posts: 3507
Location: Brussels once more ...
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| Quote: |
| Efficient block sizes can greatly reduce the amount of media needed to store the data. |
Yes, there is a gap between every block that is stored. |
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Anuj D.
Global Moderator
Joined: 22 Apr 2006
Posts: 2156
Location: Phoenix, AZ
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| expat wrote: |
| Yes, there is a gap between every block that is stored. |
And this is more paining when a media can be accessed in linear way only..such as TAPE media. |
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