When we adopted the 4*/5* naming convention in the mid-90s, I was a bit queasy about reserving so many addresses (2*4096) for CTCs, but we could afford it at the time. Since then, the number of DASD and tape devices has increased a lot.
-- At the time, we managed two data centers with two independent IODFs, so duplicate addresses were possible and in fact existed. We later merged the data centers into a single IODF, which was a very good thing but increased the number of device addresses in use as duplicates were no longer tolerable. -- We implemented DR with a strategy that requires three copies per DASD volume: primary (production), secondary (XRC copy), and tertiary (flash copy of secondary for DR images). Again, a very good thing but a gobbler of device addresses. -- Incremental increase in DASD usage over the years. Probably the smallest contributor to the increase, but as noted above, adding one volume to production is actually a three-fold increase in addresses. The advantage of any CTC naming scheme over just assigning random addresses is that a CTC can be fully identified by address alone: CEC, LPAR, and usage such as XCF vs. VTAM. The stories we heard about sysprog/operator confusion pretty much never materialized as the number of CTCs increased dramatically. . . J.O.Skip Robinson Southern California Edison Company Electric Dragon Team Paddler SHARE MVS Program Co-Manager 323-715-0595 Mobile 626-543-6132 Office ⇐=== NEW [email protected] -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Ed Jaffe Sent: Wednesday, October 17, 2018 9:40 PM To: [email protected] Subject: (External):Re: CTC conventions On 10/17/2018 6:44 PM, Jesse 1 Robinson wrote: > In hindsight I rue the decision to set aside both 4xxx and 5xxx addresses. In > practice, the low order digit is severely underused. In the beginning I > thought that we would need several different 'devices' for each LPAR. Never > actually found a need for more than four, 0 - 3. I like Rob Jackson's idea of > assigning even/odd numbers for gazinta and gazouta, or ranges like 0 - 7 and > 8 - F. Eliminating 5xxx, for example, would free up 4096 addresses for DASD. It wasn't your fault. It was IBM's recommendation. The fact is that all but one bit of position 'w' is wasted and position 'x' is nearly always underutilized in the scheme below. However, it's not uncommon at all to have more than 16 LPARs per processor making position 'y' too small in today's world. It works great for small configurations, but should be reworked for larger environments -- perhaps by combining 'w' and 'x' to a single nybble and expanding 'y' to two nybbles. CTC 4-DIGIT NAMING SCHEME: wxyz w - one nibble to distinguish gazinta from gazouta x - one nibble that uniquely represents a processor; assigned by you arbitrarily y - one nibble that represents an LPAR on processor w, such as LPAR id from HCD z - one nibble to complete device address, assigned from 0 up to F -- Phoenix Software International Edward E. Jaffe 831 Parkview Drive North El Segundo, CA 90245 https://www.phoenixsoftware.com/ ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
