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Space parameter in JCL

 
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vyasricha

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PostPosted: Wed Jul 20, 2011 4:22 pm    Post subject: Space parameter in JCL
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Hi,

I am trying to allocate the new dataset , expecting to have 500k records in file.

I am giving the allocation parameter as :
DISP=(NEW,CATLG,DELETE),SPACE=(TRK,(45,45),RLSE)

and my job ran fine with 434797 no of records . But is this will be sufficient to store 500k records ?

I know it will allocate 56664*45 = 2549880 ( primary )
56664*16*45 = 40798080 (secondary)
but this is the no of bytes it can store means 43347960
and as it is allocating the record with length of 49 so no of records= 884652.2449
Please clarify is my understanding is correct .
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expat

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PostPosted: Wed Jul 20, 2011 4:54 pm    Post subject:
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SPACE 101 for students and freshers

I assume that the RECFM=FB

27998 is the optimum BLKSIZE for a DASD dataset
INT(27998 / 49) = 571 - number of records per block
571 * 2 = 1142 records per track

I think the rest of the calculation is simple enough for you to complete icon_rolleyes.gif
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Robert Sample

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PostPosted: Wed Jul 20, 2011 4:54 pm    Post subject:
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Quote:
I know it will allocate 56664*45 = 2549880 ( primary )
56664*16*45 = 40798080 (secondary)
but this is the no of bytes it can store means 43347960
and as it is allocating the record with length of 49 so no of records= 884652.2449
Please clarify is my understanding is correct .
You are ABSOLUTELY WRONG. 56664 is the theoretical maximum number of bytes per track on a 3390 device. The actual maximum possible number of bytes to use is 55996, although it depends upon the block size and can go as low as 1892 bytes per track if the block size is 22 or less bytes. Furthermore, your calculations ignore record boundaries as well as track boundaries -- neither of which is physically possible (you cannot put 1/3 of a record on one track and 2/3 of that record on another track -- at least not easily).

Assuming SMS-managed data sets (or half-track blocking otherwise), the block size based on LRECL of 49 will be 27979. This means 571 records per block and 1142 records per track. 500,000 records will require 438 tracks (500000 divided by 1142 is 437 and a fraction -- and when calculating space, you ignore the fraction and add 1 to the integer since you cannot allocate a part of a track).

Using SPACE=(TRK,(45,45),RLSE) on such a data set means that most of the time it will run fine, but every now and then it will abend with a space issue. This is because the system only guarantees you will get the primary space allocation of 45 tracks on a disk volume. When your job attempts to acquire the other 393 tracks, 45 at a time, if the disk volume doesn't have the space available -- abend. You would be wise to increase the primary from 45 to at least 438. You might also consider allocating in cylinders instead of tracks, or even use the allocation in terms of the number of records instead of tracks.
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vyasricha

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PostPosted: Wed Jul 20, 2011 5:42 pm    Post subject:
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Thanks for the information , i was aware about the theoretical maximum numbers only. Could you please share a document / link where i can gain more knowledge on this.

Is this will be okey if i give - (trk,(438,438),rlse) ? will it work ? as i tried giving trk,(45,45) and it fine working in development region with 434797
no of records, but not working fine in production ?
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vyasricha

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PostPosted: Wed Jul 20, 2011 5:54 pm    Post subject:
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Could you guide me in how to calculate the no of records in tracks from no of records in blocks ? as i have RECORD LENGTH = 43
BLOCK SIZE = 27993 , how to calculate no of tracks for n no of records ?
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Bill Woodger

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PostPosted: Wed Jul 20, 2011 6:03 pm    Post subject: Reply to: Space parameter in JCL
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As has been explained, no-one can say that what you want to do will work. If there is not enough space on the volume for the secondary extents that you require, your job can fail.

Better, as has been said, to define the primary with enough space (plus a bit for expansion) and then you even know if you data is growing faster than expected when it goes into secondary allocation. If you rely on all the secondary extents, bear in mind you can loose a couple if the primary has to go to multiple extents.

Better to define in cylinders than tracks for anything bigger than (tracks per cylinder) tracks. Can help avoid fragmentation of the disk, even the access time a little, a 15 track extent may occupy parts of two cylinders wheras a cylinder won't - Robert, expa(r)t, I was told this a long time ago is it true? I know, google is my friend, link at the top of the page...
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Bill Woodger

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PostPosted: Wed Jul 20, 2011 6:07 pm    Post subject:
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vyasricha wrote:
Could you guide me in how to calculate the no of records in tracks from no of records in blocks ? as i have RECORD LENGTH = 43
BLOCK SIZE = 27993 , how to calculate no of tracks for n no of records ?


For fixed length, divide the magic number by record-length. Ignore the fractional part. Multiply (integer part, therefore) by record-length.

571.286 -> 571 -> 27979.

For variable, leave as 27993. You won't know beforehand how many records in any given block.
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Robert Sample

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PostPosted: Wed Jul 20, 2011 6:26 pm    Post subject:
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Google is your friend. Google GX26-4577 and you will find the 3390 Direct Access Storage Reference Summary which tells you everything you (almost) need to know about 3390 drives. In particular, Table 1 of this document tells you how many physical blocks fit into a track for the various block sizes.
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enrico-sorichetti

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PostPosted: Wed Jul 20, 2011 6:28 pm    Post subject: Reply to: Space parameter in JCL
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see here
http://www.ibmmainframes.com/viewtopic.php?t=55037&highlight=
and the discussion here
http://www.ibmmainframes.com/viewtopic.php?t=35906
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vyasricha

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PostPosted: Wed Jul 20, 2011 6:55 pm    Post subject:
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Hi,

i have gone through the link and it says that 1 trk - 56664 for 3390 device. but with reference to the reply :
"56664 is the theoretical maximum number of bytes per track on a 3390 device. The actual maximum possible number of bytes to use is 55996"

Please let me know how to proceed. i have RECORD LENGTH = 43
BLOCK SIZE = 27993 and no of records expected is 500k so what space parameter should i give ?
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enrico-sorichetti

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PostPosted: Wed Jul 20, 2011 7:02 pm    Post subject: Reply to: Space parameter in JCL
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I posted the link to different flavors of the blksize calculator,
to save some of Your time I run it for You and ...
here is the table with the capacity for different blksizes

Code:
blks3390 -      lrecl min-blksz max-blksz    blocks  min_recs  max-recs
blks3390 -         43        43        43        82        82        82
blks3390 -         43        86        86        78       156       156
blks3390 -         43       129       129        72       216       216
blks3390 -         43       172       172        69       276       276
blks3390 -         43       215       215        66       330       330
blks3390 -         43       258       258        61       366       366
blks3390 -         43       301       301        59       413       413
blks3390 -         43       344       344        57       456       456
blks3390 -         43       387       387        55       495       495
blks3390 -         43       430       430        52       520       520
blks3390 -         43       473       473        50       550       550
blks3390 -         43       516       516        49       588       588
blks3390 -         43       559       559        46       598       598
blks3390 -         43       602       602        45       630       630
blks3390 -         43       645       645        44       660       660
blks3390 -         43       688       688        43       688       688
blks3390 -         43       731       731        41       697       697
blks3390 -         43       774       774        40       720       720
blks3390 -         43       817       817        39       741       741
blks3390 -         43       860       860        37       740       740
blks3390 -         43       903       946        36       756       792
blks3390 -         43       989       989        34       782       782
blks3390 -         43      1032      1075        33       792       825
blks3390 -         43      1118      1118        32       832       832
blks3390 -         43      1161      1161        31       837       837
blks3390 -         43      1204      1247        30       840       870
blks3390 -         43      1290      1290        29       870       870
blks3390 -         43      1333      1376        28       868       896
blks3390 -         43      1419      1462        27       891       918
blks3390 -         43      1505      1548        26       910       936
blks3390 -         43      1591      1634        25       925       950
blks3390 -         43      1677      1720        24       936       960
blks3390 -         43      1763      1849        23       943       989
blks3390 -         43      1892      1935        22       968       990
blks3390 -         43      1978      2064        21       966      1008
blks3390 -         43      2107      2193        20       980      1020
blks3390 -         43      2236      2365        19       988      1045
blks3390 -         43      2408      2537        18      1008      1062
blks3390 -         43      2580      2709        17      1020      1071
blks3390 -         43      2752      2924        16      1024      1088
blks3390 -         43      2967      3139        15      1035      1095
blks3390 -         43      3182      3440        14      1036      1120
blks3390 -         43      3483      3741        13      1053      1131
blks3390 -         43      3784      4128        12      1056      1152
blks3390 -         43      4171      4558        11      1067      1166
blks3390 -         43      4601      5031        10      1070      1170
blks3390 -         43      5074      5719         9      1062      1197
blks3390 -         43      5762      6493         8      1072      1208
blks3390 -         43      6536      7525         7      1064      1225
blks3390 -         43      7568      8901         6      1056      1242
blks3390 -         43      8944     10793         5      1040      1255
blks3390 -         43     10836     13674         4      1008      1272
blks3390 -         43     13717     18447         3       957      1287
blks3390 -         43     18490     27993         2       860      1302


after that it should be quite easy to carry on the elementary math
<number of records> / 1302 ==> number of tracks needed
( at optimum blksize )
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expat

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PostPosted: Wed Jul 20, 2011 7:29 pm    Post subject:
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expat wrote:
SPACE 101 for students and freshers

I assume that the RECFM=FB

27998 is the optimum BLKSIZE for a DASD dataset
INT(27998 / 49) = 571 - number of records per block
571 * 2 = 1142 records per track

I think the rest of the calculation is simple enough for you to complete icon_rolleyes.gif

Obviously not
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