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SPACE parameter - BLK and CYL

 
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drajagopal

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Joined: 20 Jun 2006
Posts: 9

PostPosted: Tue Jun 20, 2006 3:55 pm    Post subject: SPACE parameter - BLK and CYL
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Hi,

i would like to know the relatioship b/w blocks and cylinders.
that is, how many blocks makes one cylinder?
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cpuhawg

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Joined: 14 Jun 2006
Posts: 331
Location: Jacksonville, FL

PostPosted: Tue Jun 20, 2006 6:27 pm    Post subject:
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Blocks can be any size as defined by the analyst, so there is no set number of blocks to a cylinder:

1 cylinder = 15 tracks
1 track = approximately 56,000 bytes
1/2 track = approximately 28,000 bytes

For efficiency, records should be blocked, usually half track blocking.
RECFM=FB, LRECL=80,BLKSIZE=27920
You can write 349 80 byte records in a 1/2 track, 698 80 byte records in a full track. In this case, there are two blocks to a track, 30 blocks to a cylinder.

Consider RECFM=FB,LRECL=80, BLKSIZE=800
You can write 10 80 byte records in each block, approximately 70 blocks per full track. In this case, there are 140 blocks per track, 2100 blocks per cylinder.

So a block is a segment of space on a track that will contain one or more records. In between each block is a small gap. The more blocks on track, the more gaps you have, and these gaps can use up space. If you code BLKSIZE=0 on your output dataset, the system will calculate and use the most efficient blocksize, usually half track blocking.
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drajagopal

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PostPosted: Wed Jun 21, 2006 2:05 pm    Post subject: Re: SPACE parameter - BLK and CYL
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Thank u.

I guess in the second example u gave , the no: of blocks is 1050 .
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drajagopal

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PostPosted: Wed Jun 21, 2006 2:09 pm    Post subject: Re: SPACE parameter - BLK and CYL
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Also just a clarification .........
is 1 cyn = 15 trks or 24 trks? someone told me its 24?
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prashantshinde

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Joined: 25 Nov 2005
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Location: Pune

PostPosted: Wed Jun 21, 2006 3:08 pm    Post subject:
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1 Cylinder =15 tracks
Largest blksize = 32760 bytes
A3390-n DASD storage device has capacity of 56,664 bytes per track out of which 55,996 bytes are used by application programs and rest are system specific.
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