I've finally taken the time to try to understand the numbers behind the way EAVs were implemented. I found a great discussion in the redbook "z/OS v1.12 Implimentation" SG24-7853-00 manual, chapter 20. Any time spend you happen to spend here is worth it. (not unlike all redbooks). Thanks to those that wrote it.
I did happen into a segment that makes me go hmmm. 20.4.3 Multicylinder unit section says the 21-cylinder value for the MCU is derived from being the smallest unit that can map out the largest possible EAV and stay within the index architecture (with a block size of 8192), as follows: * It is also a value that divides evenly into the 1 GB storage segments of an IBM DS8000, * These 1 GB segments are the allocation unit in the IBM DS8000 and are equivalent to 1,113 cylinders. I'm sure the "index architecture" references the index vtoc architecture, which has always been a curious archeture to me. Has this design ever been made open? Just curious as to why it made 21 the magic number? I also ran into a math issue when I divided 21 into 1GB (or 1,073,741,824/21 = 51,130,563.0476...). I suspect that's because the 1GB storage segment is a number used in the DS8000 degisn, and its really close to the 1GB value. Wondering if that's true or some other reason. Just makes me go hmmm. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
