To allocate cylinders to a dataset

meenakshi_forum · Active User Joined: 27 May 2008 Posts: 121 Location: India

Hi,

How do we determine the number of cylinders to be allocated to a dataset?

Please give me an example.

Thanks!

CICS Guy · Posted: Fri Apr 16, 2010 8:03 am

Number or records and block size and blocks per track and tracks per cylinders...

Robert Sample · Posted: Fri Apr 16, 2010 8:03 am

Find out how many records will be in the file, adjust for added records over time, and use the formulas to convert records to cylinders.

If you search this forum, you will find many examples of space calculations.

ridgewalker58 · New User Joined: 26 Sep 2008 Posts: 51 Location: New York

The Disks that we work with contain approx 57000 bytes per track and 20 tracks per cylinder. Your maximum block size can be 32768 bytes. So when I need to calculate most efficient space I usually try to stay around a DIVISABLE of 32000 bytes.

Robert Sample · Posted: Sat Apr 17, 2010 7:42 am

3390 disk drives have 56,664 bytes per track and 15 tracks per cylinder (see the 3390 reference card SX26-4577 for more details). The least wasteful block size is 27,998 bytes which allows 2 blocks per track. If you want to minimize wasted space, go with a block size close to 27,998. If you go over 27,998 you only get one block per track so using 32000 bytes per block as ridgewalker58 recommends actually reduces the amount of data that can be stored on the disk by nearly half.

Very recent releases of z/OS now allow large block sequential files which can go over 32767 bytes per block, but using this would depend upon the release of the operating system.