Last week I brought up the other TEST LPAR and went nosing. Come to find out that all the Tape Drives on both LPAR's were in Autoswitch mode. That tells me I can change all the TAPE Drives into AutoSwitch mode. Also since We are running TS Grids , once all the TAPE Drives and managed under SMS Both LPAR's will be happy and I don't need to worry about jobs fighting for TAPE Drives at 0400
Thank you all yout input -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Scott Ballentine Sent: Monday, June 2, 2025 7:37 AM To: [email protected] Subject: Re: Autoswitch Let me try to add a little more to how autoswitch works. Also check out my prior post. z/OS Allocation processing uses several levels of processing to manage autoswitchable tape drives. We primarily use ENQs (to serialize devices) and XCF communication (to share status of devices on each member of the sysplex). That's really what makes autoswitch work, at least within a sysplex. There's another level of serialization, which is at the device level, where we send assign/unassign commands to the drive so that we serialize the use of the drive. That's a hardware function, and when one system has the drive assigned, any other system that tries to issue an assign command will see the command fail. This is what prevents the drive from being used by two different sysplexes at the same time. (This is what the "ASSIGN" in the IEF292I "ASSIGNED TO FOREIGN HOST" message is referring to.) I think some of the other operating systems also use assign/unassign, but not sure that they all do. The thing to know about the assign/unassign processing is that the system has to try the assign and see if it fails in order to know if we can use the device, and we do not know when the drive is unassigned. We just have to try to assign it and see if we can use it. The XCF communication and ENQ processing is how we know that another system in the sysplex is using the drive, without having to send I/O down to the drive - when we are allocating a device, we know that a particular device is allocated to some other system in the sysplex and will just steer clear of it, rather than "try drive #1, hope it works, if not, try drive #2, etc." Assign/unassign was introduced with 3480 tape devices, so it's been around for a long time. 3490 drives added other functions that Allocation takes advantage of to make it work a little more cleanly - and of course, the TS7700's are going to emulate more modern drives anyway. With that in mind... with physical tape devices, a hardware problem tended to show up as an assign failure as well, so it was hard to distinguish a hardware problem from normal "some system outside of our sysplex is using the drive." I don't think that we see that very often with virtual drives. In most cases, I'd suggest that if you want to share drives across sysplexes, it's at least worth looking at some of those other products, such as ATAM. Not saying that Allocation's autoswitch processing won't work, but those other products were really designed for it and some might find that they work better in their environment. - Scott Ballentine ([email protected]) z/OS Allocation, Scheduler, SMF On Fri, 30 May 2025 22:12:52 +0200, Radoslaw Skorupka <[email protected]> wrote: >Maybe it's my poor English, but I'm not sure. >Paul Feller in the message below confirmed that autoswitch is working >inside the sysplex. And few sysplexes share VTS installation, but each >of the sysplexes use it's own, statically (manually) assigned set of >devices. >That's what I mean. Indeed, autoswitch between sysplex members is >working with no additional software. > >However, David - you wrote, that my understanding is/was good for real >tape drives (standalone), but TS7700 changed the game rules. That means >"foreign" (non-sysplexed) systems can autoswitch virtual tape devices >(with no additional software). Have I understood it correctly? > >AFAIK the autoswitch inside sysplex does use/require sysplex >communication. I cannot imagine why the communication is required >between sysplex members, while non-sysplexed z/OS images can autoswitch >devices with no communication. > >Exempt from z/OS 3.1 documentation: >With z/OS Release 2 and higher, the ATS STAR design improves the >availability and system management characteristics of the previous >automatic tape switching function. ATS STAR does not use the IEFAUTOS >structure but instead uses global resource serialization and XCF >services to maintain serialization when it allocates shared tape >devices. To maximize the performance of the ATS STAR function, use the >global resource serialization STAR configuration rather than the ring >configuration. > >Fun fact: I have found similar discussion in the archives of IBM-MAIN. >It was 20 years ago and I was one of the participants. :-) >A member of DFRMM development suggested IBM ATAM for cross-sysplex. >Of course it was 20 years ago, things could have changed, but I never >heard about such change. I would be happy to find some confirmation >about the change - technical details, chapter in manual, presentation, >anything. > >Regards >-- >Radoslaw Skorupka >Lodz, Poland > > > >W dniu 30.05.2025 o 14:28, Jousma, David pisze: >> Radoslaw, you said: “Yes, autoswitch does not require MIM. However >> autoswitch will not work across sysplex boundaries.” >> >> This is not correct with regards to TS7700 series tape libraries. It does >> work across sysplex boundaries without additional software. You are >> correct with regards to stand alone tape drives I believe. Not sure how >> much of that is still around though. >> >> >> >> Dave Jousma >> Vice President | Director, Technology Engineering >> >> >> >> >> >> From: IBM Mainframe Discussion List<[email protected]> on behalf of >> Radoslaw Skorupka<[email protected]> >> Date: Friday, May 30, 2025 at 8:12 AM >> To:[email protected] <[email protected]> >> Subject: Re: Autoswitch >> >> >> >> W dniu 29.05.2025 o 13:58, Jousma, David pisze: >> >>> AUTOSWITCH does NOT require GRS/MIM, etc to work inside or outside the >>> sysplex any longer. We have same tape drives online to 5 different >>> sysplexes. >> >> >> Again: it is NOT ABOUT GRS/MIM. >> >> Yes, autoswitch does not require MIM. However autoswitch will not work >> >> across sysplex boundaries. >> >> However there are software products which allow it. >> >> Product names are IBM ATAM (Automated Tape Allocation Manager) and CA-MIA. >> >> Both are licensed (and paid) products. >> >> >> >> >> >> And still, having dozens of virtual drives allow user to assign the >> >> drives statically and forget about the issue. >> >> > >---------------------------------------------------------------------- >For IBM-MAIN subscribe / signoff / archive access instructions, >send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
