That terminology morass is the reason for my declaration of terms. When we started mirroring for DR, we ran ESCON over traditional channel extenders. We did not think we could tolerate the effects synchronous delays in PPRC. Now we run FICON over DWDM in a configuration that might be suitable for PPRC, but we're not anxious to make the change.
Another reason for choosing XRC over PPRC our concern in the early 2000s that PPRC could guarantee data consistency across multiple DASD subsystems. I've heard that's no longer an issue, but again, we're not anxious to make the change. As for having a running machine at the DR site: if it's truly 'remote' and not just the other end of the building, you need a CPU to run DR systems. Our DR box is a single-engine CEC whose only role in life is DR. Because it runs no business applications, it qualifies for ZNALC licensing, which makes it very affordable. The box has enough capacity backup on demand (CBU) to run a full production workload indefinitely. We purchase CBU test intervals that allow us to turn on CBU for two 10-day periods a year for full bore testing. In between CBU tests, we are able to perform limited testing on the DR box without impacting XRC. The open systems concern is real. We have a lot of open systems that mirror via their flavor of PPRC. We all share DWDM links, but mirroring technology is different. If you want only one technology--and especially if you share DASD subsystems (we don't)--then PPRC is probably your baby. Unfortunately we have no mainframe experience with it, so my earlier advice may not be germane. . . JO.Skip Robinson Southern California Edison Company Electric Dragon Team Paddler SHARE MVS Program Co-Manager 626-302-7535 Office 323-715-0595 Mobile jo.skip.robin...@sce.com From: Tom Sims <trs...@att.net> To: IBM-MAIN@LISTSERV.UA.EDU, Date: 11/13/2013 09:45 PM Subject: Re: Global Mirror for DR Sent by: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> Thanks Skip, for the depth of the reply, which I will get to digesting in the morning! IBM seems to have muddied the terminology pool recently, and they have "Global Mirror" vs "zOS Global Mirror;" the latter formerly known as XRC and the former an unlimited-distance extension of "Metro Mirror," or PPRC. No active CPU at the remote end, implemented entirely between the controllers over >metro distances. This "Global Mirror" was considered preferable, as it requires no CPU running any licensed software at the remote end, and because it will also replicate updates to open systems data, which may or may not live in the DS8x-es in the future. Tom Sims ________________________________ From: Skip Robinson <jo.skip.robin...@sce.com> To: IBM-MAIN@LISTSERV.UA.EDU Sent: Wednesday, November 13, 2013 3:19 PM Subject: Re: Global Mirror for DR A terminology level set. By 'Global Mirror' I assume that you mean XRC, where a DFSMS task called SDM continuously transfers data updates from production disk controllers, stores the updates in journal data sets, then writes out to 'DR' DASD volumes in consistency groups. In order to 'pull' data via XRC, you need a running CPU at the DR location to host SDM. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
