Re: How to precisely calculate the number of bytes per track for a

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Subject: Re: How to precisely calculate the number of bytes per track for a
Eshudders@aol.com
Date: Fri Aug 19 2011 - 09:39:45 EDT


Hi:
 
VSAM is a little smarter than that when the CISZ can cause a large track  
fragmentation. In the case of a 32K CISZ VSAM actually uses a 16 KB physical  
record size. When it reads a CI, it actually transfers at least 2 physical  
blocks to form the 32 KB CISZ. The actual number of CIs (physical records)  
transferred depends mainly on the BUFND specified. So, you can  fit three 
16 KB records per track or 45 per cylinder.  Therefore, you  can fit 
twenty-two 32 KB CIs on a cylinder with a fragmentation of only 16  KB. If you want 
to see the physical record to CI used by VSAM, I can send  you a display 
offline. You can also look at a LISTCAT of a file to see the  physical record 
size being assigned to the CISZ selected. 
 
Regards,
Gene
 
 
In a message dated 8/19/2011 9:25:17 A.M. Eastern Daylight Time,  
g.goersch@worldnet.att.net writes:

Beth;
I have noticed that you have opened a number of topics  with this same
question, I am presuming you are anxious for an  answer.

The capacity of a 3390 track is a constant, "Every 3390 disk  volume
contains 56,664 bytes per track, 15 tracks per cylinder and  849,960
Bytes per Cylinder."  The CISIZE or BlockSize is the variable  which
determines how much data you can store on a device.

In the old  days a Blocksize was limited to 32K, if you had the
"maximum" block size of  32,0000+ bytes you could write one block per
track, this made the other  24,000 bytes useless and you wasted 2/3 of
each track.  To utilize a  dasd device to it's fullest you should use a
blocksize or CISIZE that  allows for the maximum records per track.  If
your CISIZE is the  23,552 or 45,056 you indicated you will still lose
around 10k per  track.  I like to use 18000 as a guideline, gets me 3
blocks per track  with a minimum of waste.

Hope that  helps.


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