Subject: Re: How to precisely calculate the number of bytes per track for a
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, firstname.lastname@example.org 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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