Mike, Then how did ESCON use data buffers for flow control?
Ron -----Original Message----- From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> On Behalf Of Mike Schwab Sent: Friday, June 8, 2018 3:29 PM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: [IBM-MAIN] [EXTERNAL] Re: PPRC-XD vs Async PPRC ESCON is synchronous, where after sending a buffer, it would wait for acknowledgement before sending the next buffer. FICON is async, where it sends buffer after buffer without waiting. If it doesn't get an acknowledgement within a certain time frame it would resend the lost buffer. On Fri, Jun 8, 2018 at 5:15 PM Ron hawkins <ronjhawk...@sbcglobal.net> wrote: > > Radslaw, > > Have you confused a few things when explaining the difference between > synchronous and asynchronous, and ESCON compared to FICON? > > Buffer credits are synonymous to DIBs, and a large number of buffer credits > provided by Fiber Channel switches allowed the connection to be full of > frames end to end over a greater distance than FICON. > > The buffer credits, however, did not have anything to do with reducing the > RTD spent in the "talking" as you put it. That is purely a function of two > round trips required by Fiber channel compared to 9 (I think) required by > ESCON. Buffer credits and number of DIBs affected transfer rate, not RTD. > > Asynchronous remote copy still requires the provision of adequate buffer > credits over distance to maintain line speed, where the number is a function > of line speed and distance. Having no distance related impact on response > time at any distance is the advantage of asynchronous. Synchronous cannot > guarantee zero data loss, so I struggle with coming up with advantages beyond > that myth. > > Ron > > > -----Original Message----- > From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> On Behalf Of > R.S. > Sent: Friday, June 8, 2018 3:11 AM > To: IBM-MAIN@LISTSERV.UA.EDU > Subject: Re: [IBM-MAIN] [EXTERNAL] Re: PPRC-XD vs Async PPRC > > 1. PPRC-XD and PPRC are very different animals. PPRC-XD is capable to work on > any distance, while PPRC is limited by speed of light which is not planned to > change. > 2. ESCON vs FICON did huge difference not only in speed (bit per second), but > also in something called credit buffers. In very simple word A talks to B, > but A can say many words before B acknowledge it. > Many words can be "in transit", which makes the protocol quite independend on > link length. This is better visible when A is host and B is CU (DASD or tape). > > -- > Radoslaw Skorupka > Lodz, Poland > > > > > > > W dniu 2018-06-08 o 06:10, Sankaranarayanan, Vignesh pisze: > > Hi Skip, > > > > Looks like you tried PPRC over "long distance" and had a bad exp back then. > > PPRC-XD should work fine for actual long distance, assuming that the LPAR > > itself can get an outage to let the final delta synchronize. > > > > – Vignesh > > Mainframe Infrastructure > > > > -----Original Message----- > > From: IBM Mainframe Discussion List > > [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf Of Jesse 1 Robinson > > Sent: Thursday 07-Jun-2018 23:52 > > To: IBM-MAIN@LISTSERV.UA.EDU > > Subject: [EXTERNAL] Re: PPRC-XD vs Async PPRC > > > > Data consistency was one of two reasons we chose circa 2000 to use XRC > > rather than PPRC. I know the technology has changed, and I've been *told* > > that PPRC is now capable of maintaining consistency, but I have not seen it > > in action. The other reason for XRC BTW was the synchronizing problem: we > > could not tolerate the I/O delay waiting for remote confirmation from 120 > > KM via ESCON. In 2000, everything was slower. Now we use DWDM via FICON. > > > > . > > . > > 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 > > robin...@sce.com > > > > > > -----Original Message----- > > From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On > > Behalf Of R.S. > > Sent: Thursday, June 07, 2018 4:10 AM > > To: IBM-MAIN@LISTSERV.UA.EDU > > Subject: (External):Re: PPRC-XD vs Async PPRC > > > > W dniu 2018-06-06 o 18:18, Sankaranarayanan, Vignesh pisze: > >> Hello All, > >> > >> Please could you point me to any doc explaining the differences between > >> the 2. > >> Any important, obscure, techdocs or KB page or some such as well.. ? > > Fundamental difference is data consistency. > > PPRC-XD is *inconsistent* copy during most of the time. Inconsistent is > > unusable. You have to quiesce the production and wait a little until the > > delta become zero (the copy become consistent). > > Asynchronous copy like XRC, SRDF/A, HARC is different. It is > > *consistent* copy - data on secondary site is usable, but is not current. > > Of course the time delta is small, but the most important is you don't have > > later data while earlier data is missing. > > > > -- > > Radoslaw Skorupka > > Lodz, Poland > > > > > > -------------------------------------------------------------------- > > -- For IBM-MAIN subscribe / signoff / archive access instructions, > > send email to lists...@listserv.ua.edu with the message: INFO > > IBM-MAIN > > > > MARKSANDSPENCER.COM > > ________________________________ > > Unless otherwise stated above: > > Marks and Spencer plc > > Registered Office: > > Waterside House > > 35 North Wharf Road > > London > > W2 1NW > > > > Registered No. 214436 in England and Wales. > > > > > > > ====================================================================== > > > -- > Treść tej wiadomości może zawierać informacje prawnie chronione Banku > przeznaczone wyłącznie do użytku służbowego adresata. 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