Discussion:
PPRC-XD vs Async PPRC
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Sankaranarayanan, Vignesh
2018-06-06 16:18:45 UTC
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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.. ?

- Vignesh
Mainframe Infrastructure


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Lizette Koehler
2018-06-06 19:49:54 UTC
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Have you done any internet searches with the phrase


PPRC-XD vs Async PPRC

I found many hits doing that.

Otherwise - could provide more detail of what type of information you are
looking for.


Lizette
-----Original Message-----
Sankaranarayanan, Vignesh
Sent: Wednesday, June 06, 2018 9:18 AM
Subject: PPRC-XD vs Async PPRC
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.. ?
- Vignesh
Mainframe Infrastructure
MARKSANDSPENCER.COM
________________________________
Marks and Spencer plc
Waterside House
35 North Wharf Road
London
W2 1NW
Registered No. 214436 in England and Wales.
Telephone (020) 7935 4422
Facsimile (020) 7487 2670
www.marksandspencer.com
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Sankaranarayanan, Vignesh
2018-06-07 04:22:59 UTC
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Thanks Lizette.
How about using them in the context of migrating b/w IBM boxes or IBM to other vendors, or other vendors to IBM.
What's supported, what's not, etc. ?

- Vignesh
Mainframe Infrastructure

-----Original Message-----
From: IBM Mainframe Discussion List [mailto:IBM-***@LISTSERV.UA.EDU] On Behalf Of Lizette Koehler
Sent: Thursday 07-Jun-2018 01:20
To: IBM-***@LISTSERV.UA.EDU
Subject: [EXTERNAL] Re: PPRC-XD vs Async PPRC

Have you done any internet searches with the phrase


PPRC-XD vs Async PPRC

I found many hits doing that.

Otherwise - could provide more detail of what type of information you are looking for.


Lizette
-----Original Message-----
Behalf Of Sankaranarayanan, Vignesh
Sent: Wednesday, June 06, 2018 9:18 AM
Subject: PPRC-XD vs Async PPRC
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.. ?
- Vignesh
Mainframe Infrastructure
MARKSANDSPENCER.COM
________________________________
Marks and Spencer plc
Waterside House
35 North Wharf Road
London
W2 1NW
Registered No. 214436 in England and Wales.
Telephone (020) 7935 4422
Facsimile (020) 7487 2670
www.marksandspencer.com
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Ron hawkins
2018-06-07 08:37:07 UTC
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Vignesh,

Only XRC (Global whatever for z/OS) supports migration between vendors, and
go home only works between Hitachi and IBM (or does EMC support XRC now).

Hitachi and EMC have their own FICON based migration utilities, but I am not
sure about IBM.

There are host software options for migration like FDR/PAS and TDMF.

Ron

-----Original Message-----
From: IBM Mainframe Discussion List <IBM-***@LISTSERV.UA.EDU> On Behalf Of
Sankaranarayanan, Vignesh
Sent: Wednesday, June 6, 2018 9:23 PM
To: IBM-***@LISTSERV.UA.EDU
Subject: Re: [IBM-MAIN] [EXTERNAL] Re: PPRC-XD vs Async PPRC

Thanks Lizette.
How about using them in the context of migrating b/w IBM boxes or IBM to
other vendors, or other vendors to IBM.
What's supported, what's not, etc. ?

- Vignesh
Mainframe Infrastructure

-----Original Message-----
From: IBM Mainframe Discussion List [mailto:IBM-***@LISTSERV.UA.EDU] On
Behalf Of Lizette Koehler
Sent: Thursday 07-Jun-2018 01:20
To: IBM-***@LISTSERV.UA.EDU
Subject: [EXTERNAL] Re: PPRC-XD vs Async PPRC

Have you done any internet searches with the phrase


PPRC-XD vs Async PPRC

I found many hits doing that.

Otherwise - could provide more detail of what type of information you are
looking for.


Lizette
-----Original Message-----
Behalf Of Sankaranarayanan, Vignesh
Sent: Wednesday, June 06, 2018 9:18 AM
Subject: PPRC-XD vs Async PPRC
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.. ?
- Vignesh
Mainframe Infrastructure
MARKSANDSPENCER.COM
________________________________
Marks and Spencer plc
Waterside House
35 North Wharf Road
London
W2 1NW
Registered No. 214436 in England and Wales.
Telephone (020) 7935 4422
Facsimile (020) 7487 2670
www.marksandspencer.com
Please note that electronic mail may be monitored.
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Jerry Whitteridge
2018-06-07 16:23:03 UTC
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We have always used TDMF as it's a vendor neutral solution.

Jerry Whitteridge
Delivery Manager / Mainframe Architect
GTS - Safeway Account
602 527 4871 Mobile
***@ibm.com

IBM Services
Date: 06/07/2018 01:37 AM
Subject: Re: [EXTERNAL] Re: PPRC-XD vs Async PPRC
Vignesh,
Only XRC (Global whatever for z/OS) supports migration between vendors, and
go home only works between Hitachi and IBM (or does EMC support XRC now).
Hitachi and EMC have their own FICON based migration utilities, but I am not
sure about IBM.
There are host software options for migration like FDR/PAS and TDMF.
Ron
-----Original Message-----
Sankaranarayanan, Vignesh
Sent: Wednesday, June 6, 2018 9:23 PM
Subject: Re: [IBM-MAIN] [EXTERNAL] Re: PPRC-XD vs Async PPRC
Thanks Lizette.
How about using them in the context of migrating b/w IBM boxes or IBM to
other vendors, or other vendors to IBM.
What's supported, what's not, etc. ?
- Vignesh
Mainframe Infrastructure
-----Original Message-----
Behalf Of Lizette Koehler
Sent: Thursday 07-Jun-2018 01:20
Subject: [EXTERNAL] Re: PPRC-XD vs Async PPRC
Have you done any internet searches with the phrase
PPRC-XD vs Async PPRC
I found many hits doing that.
Otherwise - could provide more detail of what type of information you are looking for.
Lizette
-----Original Message-----
Behalf Of Sankaranarayanan, Vignesh
Sent: Wednesday, June 06, 2018 9:18 AM
Subject: PPRC-XD vs Async PPRC
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.. ?
- Vignesh
Mainframe Infrastructure
MARKSANDSPENCER.COM
________________________________
Marks and Spencer plc
Waterside House
35 North Wharf Road
London
W2 1NW
Registered No. 214436 in England and Wales.
Telephone (020) 7935 4422
Facsimile (020) 7487 2670
www.marksandspencer.com
Please note that electronic mail may be monitored.
This e-mail is confidential. If you received it by mistake, please let
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Sankaranarayanan, Vignesh
2018-06-08 04:08:47 UTC
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Hi Jerry,

Replication over IP is really cool and simple; I suppose it needs the same trick to make the TDMF copy consistent as is required for PPRC-XD (quiescing all workload), in TDMF's case because it's host-based.

Let's say ther's channel extension between A <-> B, and PPRC / PPRC-XD is used.
After the migration to B, we can still use the path as a DR pathway to fail back, but with TDMF; there's no DR option available for Day-1.
So DR (basically vol replication) should have been already planned at site B before moving volumes over yonder.

- Vignesh
Mainframe Infrastructure

-----Original Message-----
From: IBM Mainframe Discussion List [mailto:IBM-***@LISTSERV.UA.EDU] On Behalf Of Jerry Whitteridge
Sent: Thursday 07-Jun-2018 21:53
To: IBM-***@LISTSERV.UA.EDU
Subject: Re: [EXTERNAL] Re: PPRC-XD vs Async PPRC

We have always used TDMF as it's a vendor neutral solution.

Jerry Whitteridge
Delivery Manager / Mainframe Architect
GTS - Safeway Account
602 527 4871 Mobile
***@ibm.com

IBM Services
Date: 06/07/2018 01:37 AM
Subject: Re: [EXTERNAL] Re: PPRC-XD vs Async PPRC Sent by: IBM
Vignesh,
Only XRC (Global whatever for z/OS) supports migration between
vendors,
and
go home only works between Hitachi and IBM (or does EMC support XRC now).
Hitachi and EMC have their own FICON based migration utilities, but I
am
not
sure about IBM.
There are host software options for migration like FDR/PAS and TDMF.
Ron
-----Original Message-----
Behalf
Of
Sankaranarayanan, Vignesh
Sent: Wednesday, June 6, 2018 9:23 PM
Subject: Re: [IBM-MAIN] [EXTERNAL] Re: PPRC-XD vs Async PPRC
Thanks Lizette.
How about using them in the context of migrating b/w IBM boxes or IBM
to other vendors, or other vendors to IBM.
What's supported, what's not, etc. ?
- Vignesh
Mainframe Infrastructure
-----Original Message-----
On Behalf Of Lizette Koehler
Sent: Thursday 07-Jun-2018 01:20
Subject: [EXTERNAL] Re: PPRC-XD vs Async PPRC
Have you done any internet searches with the phrase
PPRC-XD vs Async PPRC
I found many hits doing that.
Otherwise - could provide more detail of what type of information you are looking for.
Lizette
-----Original Message-----
Behalf Of Sankaranarayanan, Vignesh
Sent: Wednesday, June 06, 2018 9:18 AM
Subject: PPRC-XD vs Async PPRC
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.. ?
- Vignesh
Mainframe Infrastructure
MARKSANDSPENCER.COM
________________________________
Marks and Spencer plc
Waterside House
35 North Wharf Road
London
W2 1NW
Registered No. 214436 in England and Wales.
Telephone (020) 7935 4422
Facsimile (020) 7487 2670
www.marksandspencer.com
Please note that electronic mail may be monitored.
This e-mail is confidential. If you received it by mistake, please
let us know and then delete it from your system; you should not
copy, disclose, or distribute its contents to anyone nor act in
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R.S.
2018-06-07 11:10:47 UTC
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Post by Sankaranarayanan, Vignesh
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




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SWSWSWSW
2018-06-07 11:31:24 UTC
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Post by Sankaranarayanan, Vignesh
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.. ?
- Vignesh
Mainframe Infrastructure
MARKSANDSPENCER.COM
Hi Vignesh,

I have very limiteed knowledge on both XRC and SDRF/S

Here is d little Comparison

PPRC-XD(Global Copy)/SDRF-AD - Consistency not needed(SDRF-AD) and Consistency can be created by user PPRC-XD.
PPRC/SRDF-A
Global Mirror/SRDF-S
Global Mirror for z/OS - There is no host based replication soln from EMC

Apart from this, there s cascaded PPRC and cascaded SRDF soln available for long distance with no data los.

There is a Tech book called "EMC Compatibility Features for IBM Copy Services on z/OS" which gives more info

TDMF from IBM -Online data migration Procedure from EMC to IBM DASD while keeping EMC DR consistency groups active.

z/OS Migrator from EMC helps like TDMF

XRC-Migration mode also helps to migrate the data within IBM boxes. SRDF Migration also does data between VMAXs

http://www.lascon.co.uk/hwd-enterprise-disks.php#compare


Anthony
Post by Sankaranarayanan, Vignesh
________________________________
Marks and Spencer plc
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Jesse 1 Robinson
2018-06-07 18:21:57 UTC
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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
***@sce.com


-----Original Message-----
From: IBM Mainframe Discussion List [mailto:IBM-***@LISTSERV.UA.EDU] On Behalf Of R.S.
Sent: Thursday, June 07, 2018 4:10 AM
To: IBM-***@LISTSERV.UA.EDU
Subject: (External):Re: PPRC-XD vs Async PPRC
Post by Sankaranarayanan, Vignesh
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


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Ron hawkins
2018-06-08 00:29:38 UTC
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Jesse,

Round trip delay time is the same on ESCON and Fiber Channel, but the mother-may-I nature of ESCON protocols used to pump-up the droop factor, even at 10km. Fiber Channel links changed the viability of synchronous at metro distances substantially.

Personally, I think that the myth of zero data loss is not worth the performance impact when compared to asynchronous methods. By the time in-flight transactions have been rolled back the delta between application recovery times with synchronous and asynchronous is often 3/5 of 5/8 of a poofteenth.

Next time you refresh your storage, you may want to look at other asynchronous remote copy technology, as XRC is not necessarily the best option anymore (he says with a skewed POV).

Ron

-----Original Message-----
From: IBM Mainframe Discussion List <IBM-***@LISTSERV.UA.EDU> On Behalf Of Jesse 1 Robinson
Sent: Thursday, June 7, 2018 11:22 AM
To: IBM-***@LISTSERV.UA.EDU
Subject: Re: [IBM-MAIN] 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
***@sce.com


-----Original Message-----
From: IBM Mainframe Discussion List [mailto:IBM-***@LISTSERV.UA.EDU] On Behalf Of R.S.
Sent: Thursday, June 07, 2018 4:10 AM
To: IBM-***@LISTSERV.UA.EDU
Subject: (External):Re: PPRC-XD vs Async PPRC
Post by Sankaranarayanan, Vignesh
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


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Sankaranarayanan, Vignesh
2018-06-08 04:10:46 UTC
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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-***@LISTSERV.UA.EDU] On Behalf Of Jesse 1 Robinson
Sent: Thursday 07-Jun-2018 23:52
To: IBM-***@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
***@sce.com


-----Original Message-----
From: IBM Mainframe Discussion List [mailto:IBM-***@LISTSERV.UA.EDU] On Behalf Of R.S.
Sent: Thursday, June 07, 2018 4:10 AM
To: IBM-***@LISTSERV.UA.EDU
Subject: (External):Re: PPRC-XD vs Async PPRC
Post by Sankaranarayanan, Vignesh
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


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Unless otherwise stated above:
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Registered No. 214436 in England and Wales.

Telephone (020) 7935 4422
Facsimile (020) 7487 2670

www.marksandspencer.com

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R.S.
2018-06-08 10:10:59 UTC
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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
Post by Sankaranarayanan, Vignesh
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-----
Sent: Thursday 07-Jun-2018 23:52
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
-----Original Message-----
Sent: Thursday, June 07, 2018 4:10 AM
Subject: (External):Re: PPRC-XD vs Async PPRC
Post by Sankaranarayanan, Vignesh
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
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For IBM-MAIN subscribe / signoff / archive access instructions,
MARKSANDSPENCER.COM
________________________________
Marks and Spencer plc
Waterside House
35 North Wharf Road
London
W2 1NW
Registered No. 214436 in England and Wales.
======================================================================


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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: ***@mBank.plSąd 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.


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Ron hawkins
2018-06-08 22:15:46 UTC
Permalink
Raw Message
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-***@LISTSERV.UA.EDU> On Behalf Of R.S.
Sent: Friday, June 8, 2018 3:11 AM
To: IBM-***@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
Post by Sankaranarayanan, Vignesh
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-----
Sent: Thursday 07-Jun-2018 23:52
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
-----Original Message-----
Sent: Thursday, June 07, 2018 4:10 AM
Subject: (External):Re: PPRC-XD vs Async PPRC
Post by Sankaranarayanan, Vignesh
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,
MARKSANDSPENCER.COM
________________________________
Marks and Spencer plc
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: ***@mBank.plSąd 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.


----------------------------------------------------------------------
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Mike Schwab
2018-06-08 22:29:45 UTC
Permalink
Raw Message
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.
Post by Ron hawkins
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-----
Sent: Friday, June 8, 2018 3:11 AM
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
Post by Sankaranarayanan, Vignesh
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-----
Sent: Thursday 07-Jun-2018 23:52
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
-----Original Message-----
Sent: Thursday, June 07, 2018 4:10 AM
Subject: (External):Re: PPRC-XD vs Async PPRC
Post by Sankaranarayanan, Vignesh
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,
MARKSANDSPENCER.COM
________________________________
Marks and Spencer plc
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.
----------------------------------------------------------------------
For IBM-MAIN subscribe / signoff / archive access instructions,
----------------------------------------------------------------------
For IBM-MAIN subscribe / signoff / archive access instructions,
--
Mike A Schwab, Springfield IL USA
Where do Forest Rangers go to get away from it all?

----------------------------------------------------------------------
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send email to ***@listserv.ua.edu with the message: INFO IBM-MAIN
Ron hawkins
2018-06-08 23:16:45 UTC
Permalink
Raw Message
Mike,

Then how did ESCON use data buffers for flow control?

Ron

-----Original Message-----
From: IBM Mainframe Discussion List <IBM-***@LISTSERV.UA.EDU> On Behalf Of Mike Schwab
Sent: Friday, June 8, 2018 3:29 PM
To: IBM-***@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.
Post by Ron hawkins
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-----
Sent: Friday, June 8, 2018 3:11 AM
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
Post by Sankaranarayanan, Vignesh
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
Sent: Thursday 07-Jun-2018 23:52
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
-----Original Message-----
Sent: Thursday, June 07, 2018 4:10 AM
Subject: (External):Re: PPRC-XD vs Async PPRC
Post by Sankaranarayanan, Vignesh
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,
MARKSANDSPENCER.COM
________________________________
Marks and Spencer plc
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.
----------------------------------------------------------------------
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----------------------------------------------------------------------
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--
Mike A Schwab, Springfield IL USA
Where do Forest Rangers go to get away from it all?

----------------------------------------------------------------------
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Ron hawkins
2018-06-08 23:34:11 UTC
Permalink
Raw Message
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: ***@sbcglobal.net <***@sbcglobal.net>
Sent: Friday, June 8, 2018 4:17 PM
To: 'IBM Mainframe Discussion List' <IBM-***@LISTSERV.UA.EDU>
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 <IBM-***@LISTSERV.UA.EDU> On Behalf Of Mike Schwab
Sent: Friday, June 8, 2018 3:29 PM
To: IBM-***@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.
Post by Ron hawkins
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-----
Sent: Friday, June 8, 2018 3:11 AM
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
Post by Sankaranarayanan, Vignesh
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
Sent: Thursday 07-Jun-2018 23:52
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
-----Original Message-----
Sent: Thursday, June 07, 2018 4:10 AM
Subject: (External):Re: PPRC-XD vs Async PPRC
Post by Sankaranarayanan, Vignesh
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,
MARKSANDSPENCER.COM
________________________________
Marks and Spencer plc
Waterside House
35 North Wharf Road
London
W2 1NW
Registered No. 214436 in England and Wales.
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Mike A Schwab, Springfield IL USA
Where do Forest Rangers go to get away from it all?

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Jesse 1 Robinson
2018-06-08 23:21:16 UTC
Permalink
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I am absolutely not a hardware guy, so I tend to reduce hardware issues to simpler terms. First off, mirroring motivation was not part of this thread initially, so I didn't point out that our entire business case for mirroring was Disaster Recovery. Any technology that depends on 'letting things finish' to catch up at the remote side is ruled out. When the meteorite falls or the earthquake hits or the volcano blows its top, there is no data reconciliation grace period. We got what we got and nothing more. Data consistency is far more important than data currency.

So we started with XRC around 2000 using ESCON devices over 'conventional channel extension'. I believe the vendor was CNT but cannot find any doc. We never seriously considered PPRC--at the time only synchronous--because of distance (~ 120 KM) and the aforementioned need for data consistency. The killer was ESCON protocol, not circuit speed, which XRC can live with but not PPRC. A synchronous technology will slow down production I/O to allow remote I/O to complete. That impact was not acceptable.

Then along came DWDM, which promised to free us from vendor tentacles and monthly bills. But ESCON over DWDM was a disaster, far slower than the alternative. So we plunged headlong into the still evolving FICON arena. It was a bumpy road, but we eventually got it working. ESCON switches were replaced with FICON switches. Over the years everything has gotten faster and nimbler.

BTW despite the dominance of DR in the equation, we used the same technology for two separate data center moves. In both cases, we went into a 'DR exercise' but stayed put in the new location. In other words, a DR solution can work for planned relocation, but not necessarily vice versa.

.
.
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
***@sce.com


-----Original Message-----
From: IBM Mainframe Discussion List [mailto:IBM-***@LISTSERV.UA.EDU] On Behalf Of Mike Schwab
Sent: Friday, June 08, 2018 3:29 PM
To: IBM-***@LISTSERV.UA.EDU
Subject: (External):Re: [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.
Post by Ron hawkins
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-----
Sent: Friday, June 8, 2018 3:11 AM
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
Post by Sankaranarayanan, Vignesh
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
Sent: Thursday 07-Jun-2018 23:52
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
-----Original Message-----
Sent: Thursday, June 07, 2018 4:10 AM
Subject: (External):Re: PPRC-XD vs Async PPRC
Post by Sankaranarayanan, Vignesh
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.
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Radoslaw Skorupka
Lodz, Poland
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