IBM Mainframe Forum

Hi, I need some information on extended format VSAM dataset and how to calculate the space requirement so as to avoid frequent CA/CI splits.

I have a 95 char KSDS with first 12 char's as KEY.
There are approximately 81 Million records that need to be loaded into this VSAM from a flat file. This of course will keep growing once implemented.

a. How to calculate the approximate space of the cluster to be defined keeping in mind the current and future requirements? Is this different than the standard VSAM?

I did refer the IBM manuals but its not really very helpful:
http://publib.boulder.ibm.com/infocente ... c18022.htm

Will you be using the VSAM compression features as well as the extended 4Gb capabilities. If you use the compression facility the compression ratio depends entirely on the how the data is represented and can vary as records are deleted or added, so that sort of blows an initial estimate out of the water.

It is the FREESPACE parameters that help in reducing the number of CI / CA splits by providing some freespace to insert new records into without creating a split.

Your best bet would be to see the initial usage of the dataset with and without compression, using varying FSPC parameters, and once you are reasonably happy, to monitor as it gets used more and more used, making adjustments if required.

As for avoiding splits, with the speed of modern DASD subsystems this hardly causes much difference, and it is claimed none at all with RAID 6 technology DASD. The main reason I bother to reorg a dataset is the number of extents.

Thank you expat for your reply. We are not using compression but just extended addressability so that we can address beyond 4G.

Can you give me some idea regarding the space calculation (in terms of CYLS) based on the data provided in my original post.

Please give me some information if you aware of any additional parameters that need to be defined when the extended format VSAM cluster is being defined/created.
Thank you again.

You need to go talk with your storage management people to find out the DATACLAS and STORCLAS to use with extended format VSAM files.

There may be one setup for extended compressed and extended noncompressed. Only your storage people will know. However, for files over 4Gb it is unusual to have them uncompressed.

As for a space calculation, it's been a long time since I done this for a VSAM file, I usually go for a "finger in the air" value, see the results, and then adapt. I will try and find the formula for VSAM calculations if I still have it.

Expat - Thank you again for your reply.

I have not really done space calculations before so I will really appreciate if you can provide some insight into it.