Mike, Excuse my flippant reply earlier. Are you confusing "one frame at a time" with ESCON's path ownership and "one IO at a time?"
Both ESCON and Fiber Channel use receiving buffers and ACK responses to control the number of in-flight frames, or DIBs in the channel. Both protocols will send frames until the frames in flight is equal to the number of buffers that the receiving port can handle. The transmitter then waits for an ACK from the receiver before sending the next frame. If there are enough buffers for the link to be full of frames end-to-end across the distance, then data streams continuously from port to port. ESCON cannot match the throughput of multiple IO on a channel, but that is not an architectural limitation caused by the number of ESCON data buffers or Fiber Channel buffer credits. My memory may be hazy on this, but I think a lost frame on ESCON would cause retransmission of all the frames in an IO. I need to find Dr Pat's old DIB paper. Ron -----Original Message----- From: [email protected] <[email protected]> Sent: Friday, June 8, 2018 4:17 PM To: 'IBM Mainframe Discussion List' <[email protected]> Subject: RE: [IBM-MAIN] [EXTERNAL] Re: PPRC-XD vs Async PPRC Mike, Then how did ESCON use data buffers for flow control? Ron -----Original Message----- From: IBM Mainframe Discussion List <[email protected]> On Behalf Of Mike Schwab Sent: Friday, June 8, 2018 3:29 PM To: [email protected] 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 <[email protected]> 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 <[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. Jeżeli nie jesteś > adresatem niniejszej wiadomości lub pracownikiem upoważnionym do jej > przekazania adresatowi, informujemy, że jej rozpowszechnianie, kopiowanie, > rozprowadzanie lub inne działanie o podobnym charakterze jest prawnie > zabronione i może być karalne. Jeżeli otrzymałeś tę wiadomość omyłkowo, > prosimy niezwłocznie zawiadomić nadawcę wysyłając odpowiedź oraz trwale > usunąć tę wiadomość włączając w to wszelkie jej kopie wydrukowane lub > zapisane na dysku. > > This e-mail may contain legally privileged information of the Bank and is > intended solely for business use of the addressee. This e-mail may only be > received by the addressee and may not be disclosed to any third parties. If > you are not the intended addressee of this e-mail or the employee authorized > to forward it to the addressee, be advised that any dissemination, copying, > distribution or any other similar activity is legally prohibited and may be > punishable. If you received this e-mail by mistake please advise the sender > immediately by using the reply facility in your e-mail software and delete > permanently this e-mail including any copies of it either printed or saved to > hard drive. > > mBank S.A. z siedzibą w Warszawie, ul. Senatorska 18, 00-950 Warszawa, > www.mBank.pl, e-mail: [email protected]ąd Rejonowy dla m. st. Warszawy XII > Wydział Gospodarczy Krajowego Rejestru Sądowego, nr rejestru przedsiębiorców > KRS 0000025237, NIP: 526-021-50-88. Według stanu na dzień 01.01.2018 r. > kapitał zakładowy mBanku S.A. (w całości wpłacony) wynosi 169.248.488 złotych. > > > ---------------------------------------------------------------------- > 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 -- Mike A Schwab, Springfield IL USA Where do Forest Rangers go to get away from it all? ---------------------------------------------------------------------- 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
