Calculate the number of cylinders required for given records of file?

[Kotak]

Hi,

I have a file having 70,000 records. How can I calculate how many cylinders of storage will it take? Any guide on that would help.

[nicc]

Cylinders are for disk data sets not files.
If you wanto calculate the space required it is, roughly, records * lrecl / approx, bytes per half track / (number of tracks per cylinder * 2).
And all that is found in various places by doing a simple search.

And you really need to get a link to the 3390 reference card.

[Robert Sample]

Saying you want to know the number of cylinders 70,000 records needs is like asking "how high is up?" Unless you provide the record length, the question cannot be answered -- 70,000 records that are 32750 bytes each will take a lot more cylinders than 70,000 records that are 18 bytes each.

Either bookmark this page or download it: https://archive.org/details/bitsavers_i ... n89_689419 so you'll never again have to ask how many cylinders X records need.

[Kotak]

It was LRECL=80 and FB.

Downloaded that file and it talks about geometry. Should we be knowing the geometry of the DASD too while calculating the cylinders??

[nicc]

No - the number of bytes in a 3390 track/cylinder is the same whatever, if you read the card.

[Robert Sample]

Downloaded that file and it talks about geometry. Should we be knowing the geometry of the DASD too while calculating the cylinders??

Note that the original reference card was published in 1989; over the last 28 years there have been a few changes. Don't worry about the geometry, and use the table WITHOUT keys. Half-track blocking is 27998 bytes, so divide 27998 by 80 (your record length) and discard the fraction. That tells you how many records will fit into half a track. Double it for tracks and multiply by 15 to get cylinders. Divide the result into your number of records and round up (that is, a division result of 6.001 would become 7). That is the number of cylinders needed.