Search390.com Expert Question of the Week September 24, 2001 =================================================== SPONSORED BY: Postmaster Direct =================================================== GET THE INFO YOU WANT TODAY What do YOU want in your e-mailbox? How about FREE info and offers about computers, networking, wireless devices, finance and lots more? Visit http://search390.techtarget.com/postmasterDirect/, choose the topics that interest you, and you'll get the e-mail you want. =================================================== --------------------------------------------------- Welcome to Search390's Expert Question of the Week newsletter. Remember, no question is too simple for Ask the Experts! If you have a 390-related question, send it to [EMAIL PROTECTED] Selected questions will be answered by our experts. This week's question was answered by Gerhard Adam, search390's Systems Management Expert. THIS WEEK'S QUESTION: Q: Given the historical problems associated with disk enq & reserve lockouts on OS/390 systems and the subsequent feature developments of software monitors such as TMON, will there be an exacerbation of these problems when PAV's are robustly implemented on large OS/390-z/OS environments? If so, what would you suggest operators/sysprogs do to minimize the impact? The overall scenario is that there is a small, finite amount of time to debug a enq/reserve lockout, prior to management decision to IPL to clear the issue. I'm implying that a longer enq/reserve list will take a correspondingly longer time to debug, during a live situation. Also, what pro/con situations do you see with the new SYNCRES(yes) GRS parm that affects the order of the enq/reserve processing? A: Well, let me begin by answering the last part of your question first. The SYNCHRES parm has been available since OS/390 Rel 7 and its primary use is to ensure that a hardware reserve is successfully executed before a GRS ENQ is issued. The intent is to avoid deadlocks that might occur by having an ENQ outstanding and yet be unable to complete RESERVE processing against the device. Since the RESERVE doesn't take effect until the first I/O is issued, this approach is a reasonable way of reducing the potential for deadlocks. PAV's are intended to provide simultaneous access to a volume from a single system thus reducing IOSQ time. The primary consideration is that the domain over which the I/O operates (ie: the extents) don't conflict. In the case of WRITE operations, serialization will still occur for channel commands operating within the same domain. Multiple Allegiance is the ESS feature that deals with the issue of I/O operations occurring across systems. In this case, there is no problem unless the I/O conflicts with a RESERVE. If a RESERVE occurs, the other channel commands would be queued in the ESS. As to GRS ENQ/RESERVE processing, I don't see how adding PAV's or other storage devices will make any difference to ENQ resolution scenarios. Since the conflicts that may or may not occur would occur today. I'm not sure why you think the ENQ/RESERVE list should get any longer. Since the ESS features are designed to allow greater concurrency of operation, this wouldn't result in higher levels of ENQ/RESERVE competition. In other words, PAV and MA are intended to minimize delays that already exist; not increase workloads. ------------------------------------------------------------ Gerhard Adam is this week's featured expert. If you have a question for Gerhard, you can submit it here: http://search390.techtarget.com/ateQuestion/0,289624,sid10_cid365820_tax285033,00.html If you have performance management questions, start posting them in our Operating Systems forum. Remember, Senior Technical Consultant and Performance and Workload Management Expert Steve Samson will be live in the OS forum this Friday, Sept 28 from 3:00 pm EDT to 4:00pm to answer your questions. To post a question for Steve, go to: http://search390.discussions.techtarget.com/WebX?50@@.ee83ff6 ========================================================== THIS WEEK'S search390 FEATURED TOPIC: Backup and recovery ========================================================== Natural and sometimes not so natural disasters can bring your systems down. But there are steps you can take to ensure a smooth recovery. 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