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 <[email protected]> On Behalf Of R.S. Sent: Friday, June 8, 2018 3:11 AM To: [email protected] 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:[email protected]] On > Behalf Of Jesse 1 Robinson > Sent: Thursday 07-Jun-2018 23:52 > To: [email protected] > 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 > [email protected] > > > -----Original Message----- > From: IBM Mainframe Discussion List [mailto:[email protected]] On > Behalf Of R.S. > Sent: Thursday, June 07, 2018 4:10 AM > To: [email protected] > 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 [email protected] 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. Odbiorcą może być jedynie jej adresat z wyłączeniem dostępu osób trzecich. 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