MVSFORUMS.com

mvenkatesha · Posted: Tue Oct 10, 2006 3:06 am Post subject:

Can any one Please explain me how Block size, Logical record length and record format are defined with respect to blocks, tracks and cylinders. I am very much confused with this. I just allocate data set without knowing above facts
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murthy

kolusu · Posted: Tue Oct 10, 2006 8:42 am Post subject:

mvenkatesha,

Did you read the first post in this topic ?

Kolusu
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mvenkatesha · Posted: Wed Oct 11, 2006 2:02 am Post subject:

Johann,

The first posting by you is great help for me. This really helped me to allocate the datasets of sufficient size and handling memory efficiently.

Can I get more theoretical information relating to catalog, volume serial, allocation of datasets, Block size, Logical record length, record format, blocks, tracks and cylinders. I am very much confused with this.

I know how to calculate space (cyl, trk, blk) if I know the record length and amount of records. But how actually mvs handles above stuff I am really confused. Can you please provide a link or a document where above stuffs are clearly explained.

Sorry for taking your time but this is really bugging my head from the day I entered mainframes.
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murthy

Bill Dennis · Posted: Wed Oct 11, 2006 8:34 am Post subject:

In the DFSMS set of manuals is one called "Using Data Sets" which explains a lot about tape and disk space and dataset allocations. Check it out.
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Bill Dennis

Disclaimer: My comments on this foorum are my own and do not represent the opinions or suggestions of any other person or business entity.

kolusu · Posted: Wed Oct 11, 2006 8:39 am Post subject:

serobinson · Beginner Joined: 22 Sep 2006 Posts: 11 Topics: 5

I found this space calculator on another website. It looks promising. I

Bill Dennis · Posted: Mon Dec 04, 2006 10:11 am Post subject:

Beware: At first glance, this utility doesn't appear to account for the overhead lost in the physical data recording. The physical block sizes written and inter-block waste mean that you can't just divide logical blksize into the max bytes per trk!

For a link to a 3390 capacities table, click here http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/am3u1001/B.1.2
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Regards,
Bill Dennis

Disclaimer: My comments on this foorum are my own and do not represent the opinions or suggestions of any other person or business entity.

ranga_subham · Intermediate Joined: 31 Jan 2006 Posts: 255 Topics: 72

Hi,

Do you specify AVGREC=K or U when you calculate space based on BLKSIZE?

I have written new cobol program that processes several inputs and writes one output file. The specification given was to calculate the space for output dataset to hold 1,00,000 (max records). So, in this case how do I calculate the space using both these techniques?

The specifications are

LRECL=356, RECFM=FB & LRECL=360 & RECFM=VB

1) Using the block size?
2). Using the LRECL?

Please explain.

TIA.
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Ranga
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None of us is as smart as all of us - Ken Blanchard

Mervyn · Posted: Wed Jan 10, 2007 10:12 am Post subject:

ranga_subham,

The simplest way to code the SPACE parameter in your JCL is to use the LRECL and the number of records you expect.

For FB, I'd probably code:

SPACE=(356,(50,50),RLSE),AVGREC=K

This would request 50,000 records of 356 bytes in each extent, and would release any unused space.

For VB, I'd have to consider what the average record length actually was, and use that instead of the 356. If in doubt, I'd leave the SPACE parameter as it is, or change 356 to 360.

There is usually no need to code BLKSIZE at all, but you may want to code BLKSIZE=0 to make it obvious that the System Determined Blocksize is to be used. Some shops may also need DSORG=PS.
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kolusu · Posted: Wed Jan 10, 2007 10:20 am Post subject: Re: AVGREC / BLKSIZE

Bill Dennis · Posted: Thu Jan 11, 2007 11:23 am Post subject:

The answer is based on physical block size and how many records fit in that blksize?

It's easy to be exact with RECFM=FB records. If your "RECFM=VB" records can be shorter than 360, then you need to know the average record size. Compute how many would fit in a half-track block and how many blocks are needed based on device. Add a little more because it's an estimate for VB files.
_________________
Regards,
Bill Dennis

Disclaimer: My comments on this foorum are my own and do not represent the opinions or suggestions of any other person or business entity.

ranga_subham · Intermediate Joined: 31 Jan 2006 Posts: 255 Topics: 72

Thanks Mervyn.

Kolusu, I've started reading this topic from top and in the middle i've found that you made some corrections that were told by Bill Dennis. I could not make out whether those corrections are reflecting here or not........ Sad

That is all I can say....

Thanks.
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Ranga
*****
None of us is as smart as all of us - Ken Blanchard

dohellwithmf · Beginner Joined: 12 Jul 2007 Posts: 55 Topics: 23

How can we code whether we need Full track blocking or half track blocking? Is it user provided input or depends upon the installation?

Nic Clouston · Posted: Tue May 13, 2008 7:33 am Post subject:

(Almost) always use 1/2 track blocking. That is done by making your blocksize as near to the size of 1/2 a track. as possible without exceeding that size.
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