Go into ISPF and browse the physical file to which the database area maps as if you were browsing a normal flat file.
In the ISPF display, each database page will appear as one line.
You will notice that the first line is noticeably different to the other lines. This is because it is a SPACE MANAGEMENT PAGE (SMP) and it consists solely of a series of two-byte binary values. Most of these two-byte values will be the same. For example, the first line here in red is the first SMP:
Turn HEX ON and note the first four bytes in the line:
In this case the first four bytes are 00030D41.
This is the page number in hexadecimal. X’00030D41’ is 200001.
Turn HEX OFF.
Now what you need to do is scroll forward in the file (PF8) and find the next sequential SMP. It will appear similar to the first one, with many, possibly repeating, two-byte binary values. Typically this could be several thousand lines (50 pages) or more.
When you have found the next SMP, turn HEX ON again and note the page number.
In this example, the next SMP was found here:
The page number is x’0003158B’ or 202123.
Now take the difference between these two page numbers, multiply by 2 and add 32.
(202123 – 200001) * 2 + 32 = 4276.
So the ORIGINAL PAGE SIZE clause for this database area is, or should be, 4276.