Re: How do XCF couple datasets get serialized in a sysplex?

2011-05-29 Thread Giliad Wilf 
On Fri, 27 May 2011 07:02:30 -0500, Bill Neiman  wrote:

>XCF does not use any of the interfaces that establish a reserve on a
>device - not ENQ / RESERVE in any of its external implementations, nor the
>Device Reserve (B4) command.
>
> The reference to device-level serialization in my earlier append wasn't
>really correct.  More precisely, XCF uses appropriate device commands to
>establish data set-level serialization to prevent interleaving of channel
>programs from multiple systems.  We do not reserve an entire device.
>
> Bill Neiman
> Parallel Sysplex development, IBM
>
 
 
Thank you Bill for the clarification

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Re: How do XCF couple datasets get serialized in a sysplex?

2011-05-27 Thread Bill Neiman 
XCF does not use any of the interfaces that establish a reserve on a
device - not ENQ / RESERVE in any of its external implementations, nor the
Device Reserve (B4) command.

 The reference to device-level serialization in my earlier append wasn't
really correct.  More precisely, XCF uses appropriate device commands to
establish data set-level serialization to prevent interleaving of channel
programs from multiple systems.  We do not reserve an entire device.

 Bill Neiman
 Parallel Sysplex development, IBM

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Re: How do XCF couple datasets get serialized in a sysplex?

2011-05-27 Thread Giliad Wilf 
On Wed, 25 May 2011 07:04:04 -0500, Bill Neiman  
wrote:

>...
>XCF uses several types of serialization to protect couple data sets.
>But to clear up one misconception right away:  Hardware reserves are 
*NEVER*
>used to serialize couple data sets.
>...
 
Thank you Bill.
 
One last question:
When you wrote "Hardware reserves are *NEVER* used to serialize couple data 
sets", did you mean "Neither ISGENQ, nor RESERVE macros are ever being used" 
?
 
Could this mean that maybe device reserve (channel command code B4, 
properly positioned within a channel program) is being directly used ?
After all, how else could sole, exclusive access to a device be guaranteed to a 
specific system ? 
 
We do not intend to reverse-engineer, mimic, or otherwise fiddle or interfere 
with any IBM internal unpublished protocol.
We just want to understand.

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Re: How do XCF couple datasets get serialized in a sysplex?

2011-05-26 Thread Shmuel Metz (Seymour J.) 
In , on 05/25/2011
   at 11:01 AM, Binyamin Dissen  said:

>Reserve is a hardware function which is exposed via ENQ.

More precisely, the ENQ and RESERVE macros issue the same SVC, with
different options in the parameter lists.
 
-- 
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 ISO position; see  
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Re: How do XCF couple datasets get serialized in a sysplex?

2011-05-25 Thread R.S. 

W dniu 2011-05-25 15:37, Art Gutowski pisze:

On Tue, 24 May 2011 13:26:45 +0200, R.S.
  wrote:


Just to complement Barbara's excellent anwser:
One of the reasons why CDS datasets should reside on separate volumes is
hardware RESERVE. It is used for CDSes, at least in some situations.


and,
On Wed, 25 May 2011 07:04:04 -0500, Bill Neiman
wrote:


XCF uses several types of serialization to protect couple data sets.
But to clear up one misconception right away:  Hardware reserves are
*NEVER* used to serialize couple data sets.


To hopefully clarify, the isolation of CDSes to avoid RESERVE is to prevent a
RESERVE for *other* datasets residing on the volume, thus locking out sysplex
functions, most importantly, XCF.


I stand corrected. Thank you.
However I could swear that such information (about RESERVEs) was 
provided during sysplex course ;-(((


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Re: How do XCF couple datasets get serialized in a sysplex?

2011-05-25 Thread Art Gutowski 
On Tue, 24 May 2011 13:26:45 +0200, R.S. 
 wrote:

>Just to complement Barbara's excellent anwser:
>One of the reasons why CDS datasets should reside on separate volumes is
>hardware RESERVE. It is used for CDSes, at least in some situations.

and,
On Wed, 25 May 2011 07:04:04 -0500, Bill Neiman  
wrote:

>XCF uses several types of serialization to protect couple data sets.
>But to clear up one misconception right away:  Hardware reserves are 
>*NEVER* used to serialize couple data sets.

To hopefully clarify, the isolation of CDSes to avoid RESERVE is to prevent a 
RESERVE for *other* datasets residing on the volume, thus locking out sysplex 
functions, most importantly, XCF.  

Regards,
Art Gutowski
Compuware Corporation

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Re: How do XCF couple datasets get serialized in a sysplex?

2011-05-25 Thread Bill Neiman 
XCF uses several types of serialization to protect couple data sets. 
But to clear up one misconception right away:  Hardware reserves are *NEVER*
used to serialize couple data sets.

 As Barbara Nitz noted, CDSes are dynamically allocated, and the
attendant ENQ serves to prevent inadvertent deletion of the data set.  Other
than that, there are no ENQs involved.  There is (1) device-level
serialization to ensure that channel programs initiated from two different
systems cannot interleave if either of them is updating the CDS, (2)
system-level serialization to ensure that only one request from a given
system is accessing a particular CDS record at a time, and (3) record-level
serialization to ensure that only one system at a time can update any given
CDS record.

 Bill Neiman
 Parallel Sysplex Development, IBM

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Re: How do XCF couple datasets get serialized in a sysplex?

2011-05-25 Thread Binyamin Dissen 
On Tue, 24 May 2011 07:06:04 -0500 Giliad Wilf  wrote:

:>On Tue, 24 May 2011 13:26:45 +0200, R.S. 
:> wrote:

:>>Just to complement Barbara's excellent anwser:
:>>One of the reasons why CDS datasets should reside on separate volumes is
:>>hardware RESERVE. It is used for CDSes, at least in some situations.

:>Indeed, may be the SYSDSN ENQs we see are not the result of XCFAS 
:>dynamically allocating couple datasets via SVC99. Maybe these ENQs are 
:>explicitly being issued to prevent accidental deletion of these datasets, 
much 
:>the same way that LINKLIST datasets get handled by XCFAS.
 
:>However, you wrote "It is used for CDSes, at least in some situations".
:>How do you know that couple datasets get serialized by RESERVEs?
:>What is the QNAME for these RESERVEs?

Reserve is a hardware function which is exposed via ENQ. System components
probably avoid the ENQ overhead.

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Re: How do XCF couple datasets get serialized in a sysplex?

2011-05-24 Thread Giliad Wilf 
On Tue, 24 May 2011 13:26:45 +0200, R.S. 
 wrote:

>
>Just to complement Barbara's excellent anwser:
>One of the reasons why CDS datasets should reside on separate volumes is
>hardware RESERVE. It is used for CDSes, at least in some situations.
>
>--
>Radoslaw Skorupka
>Lodz, Poland
>
 
Indeed, may be the SYSDSN ENQs we see are not the result of XCFAS 
dynamically allocating couple datasets via SVC99. Maybe these ENQs are 
explicitly being issued to prevent accidental deletion of these datasets, much 
the same way that LINKLIST datasets get handled by XCFAS.
 
However, you wrote "It is used for CDSes, at least in some situations".
How do you know that couple datasets get serialized by RESERVEs?
What is the QNAME for these RESERVEs?

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Re: How do XCF couple datasets get serialized in a sysplex?

2011-05-24 Thread R.S. 

W dniu 2011-05-24 12:07, Giliad Wilf pisze:

Hi All,

We are trying to figure out how do XCF couple datasets get serialized in a
sysplex.

We can see there is a SYSDSN shared SYSTEM(*) ENQs on each sysplex
member system, but seems this is only the result of XCFAS doing dynamic
allocation for them when the system is being IPLed.

So, there must be another serialization protocol that ensures that all sysplex
member systems can simultaneously access these datasets safely both for read
and for write.

Can someone shed some light on this issue?


Just to complement Barbara's excellent anwser:
One of the reasons why CDS datasets should reside on separate volumes is 
hardware RESERVE. It is used for CDSes, at least in some situations.


--
Radoslaw Skorupka
Lodz, Poland


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Re: How do XCF couple datasets get serialized in a sysplex?

2011-05-24 Thread Barbara Nitz 
>We can see there is a SYSDSN shared SYSTEM(*) ENQs on each sysplex
>member system, but seems this is only the result of XCFAS doing dynamic
>allocation for them when the system is being IPLed.
As far as I know, those ENQs are purely there so you cannot shoot yourselves
in the foot and delete the active CDS while it is in use (which would result
in a CDS switch at best and a wait stated sysplex at worst). Those ENQs have
nothing to do with the actual serialization.

>So, there must be another serialization protocol that ensures that all sysplex
>member systems can simultaneously access these datasets safely both for read
>and for write.
The actual serialization is done via an IBM internal protocol. After all,
*that* serialization must work lng before GRS is even active on any
system. The serialization ensures that *one* system at a time can write
without corrupting the CDS.

>We only see SYSTEM scope, and may be this is to be
>attributed to CA-MIM being started later after IPL moment
We are not using MIM, and ours are SYSTEMS scope (in a true sysplex), and
SYSTEM scope in a monoplex with GRS=none.

Regards, Barbara Nitz

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How do XCF couple datasets get serialized in a sysplex?

2011-05-24 Thread Giliad Wilf 
Hi All,
 
We are trying to figure out how do XCF couple datasets get serialized in a 
sysplex.
 
We can see there is a SYSDSN shared SYSTEM(*) ENQs on each sysplex 
member system, but seems this is only the result of XCFAS doing dynamic 
allocation for them when the system is being IPLed.
 
So, there must be another serialization protocol that ensures that all sysplex 
member systems can simultaneously access these datasets safely both for read 
and for write.
 
Can someone shed some light on this issue?
 
 
(*) Note: We suspect these SYSDSN ENQs we see, should have been changed 
to SYSTEMS scope. We only see SYSTEM scope, and may be this is to be 
attributed to CA-MIM being started later after IPL moment, and not modifying 
ENQs issued before its startup. I assume that if we were relying on GRS alone, 
an RNL definition would have changed SYSTEM into SYSTEMS, but I'm not sure 
whether leaving it SYSTEM could risk something, as we never seen couple 
datasets getting corrupted.

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