Lock and SCA duplexed

Jose Antonio

Lock and SCA duplexed
Hi everyone!



Is it worthy to have SCA and Lock structures duplexed under Data Sharing? We have it but we are thinking of changing it to simplexed

structures.



Thanks for your help!!!



__________________________
José A Morcillo Valenciano
Tfno.: +34 965 90 51 43
747-Producción Informática

< http://www.cam.es/ >

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Robert Catterall

Re: Lock and SCA duplexed
(in response to Jose Antonio)
Jose,

That depends in part on your parallel sysplex / data sharing configuration.
Going to non-duplexed lock and SCA structures is probably a good idea if
these structures are NOT in the same "box" as a DB2 subsystem that
participates in the associated DB2 data sharing group. In that case,
duplexing the structures imposes an overhead cost and delivers little in the
way of availability benefits. If you are not duplexing the structures and
you lose the CF LPAR holding the structures, they'll be automatically
rebuilt quickly (if you have your structure failure management, or SFM,
policy set up for automatic rebuild in case of a loss of connectivity to the
structures) and you'll be back to normal again with just a temporary
workflow slowdown during the lock structure and SCA rebuild operation.

If your lock and SCA structures are in a CF LPAR that is in the same "box"
as a z/OS system in which a member of the associated DB2 data sharing group
runs, and if these structures are not duplexed, you have a small risk of an
occurrence of the so-called "double failure" scenario: if that box (and I
mean the whole server -- not just the CF LPAR or a z/OS LPAR) fails, you've
lost the lock structure and the SCA, AND a member of the data sharing group.
Because information from all group members is needed for lock structure and
SCA rebuild, the structures won't be rebuilt (because a member was lost when
the structures were lost). Because a data sharing group can't operate
without the lock structure and the SCA, you'll have a group failure and
you'll need a group restart to get going again.

If that second paragraph describes your configuration, the duplex/don't
duplex decision will very much depend on your availability requirements. If
you don't duplex the lock structure and the SCA, you could experience the
double-failure scenario. The things to keep in mind are:

1. The double-failure scenario is VERY unlikely to occur. Remember, you'd
have to lose the entire System z server that holds the CF LPAR with the lock
structure and the SCA and also holds a z/OS LPAR with an associated data
sharing group member. Losing a CF LPAR or a z/OS LPAR is a rare enough
event, but losing an entire mainframe server? It's possible, but the odds of
it happening are very low.
2. If the double-failure does occur and you have to restart the data
sharing group, that operation is likely to complete within a small number of
minutes (assuming that you're duplexing the group buffer pools -- you
DEFINITELY want to do that so as to avoid having a lot of objects go into
group buffer pool recover pending status).

So, if you have the "paragraph 2" configuration, and you decide to not
duplex the lock structure and the SCA, you'll face a very small risk of a
scenario that would result in a system outage that would probably have a
duration of a few minutes. If you're OK with that (and many organizations
are), go with simplexed lock and SCA structures. If you're not OK with that
(and some organizations are not), continue to duplex the structures so as to
eliminate the double-failure possibility.

Robert


On Thu, Feb 4, 2010 at 6:37 AM, Jose Antonio <[login to unmask email]> wrote:

> Hi everyone!
>
>
>
> Is it worthy to have SCA and Lock structures duplexed under Data Sharing?
> We have it but we are thinking of changing it to simplexed
>
> structures.
>
>
>
> Thanks for your help!!!
>
>
>
> __________________________
> José A Morcillo Valenciano
> Tfno.: +34 965 90 51 43
> 747-Producción Informática
>
> < http://www.cam.es/ >
>
> __________________________
>
>
>
>
>
> Este correo electrónico es confidencial. Si lo ha recibido por error, por favor
> contacte con el remitente y destruya su contenido. Toda la información relativa a
> la Protección de Datos de Carácter Personal, se encuentra a su disposición en la
> página web www.cam.es , en el apartado Aviso legal
>
> This e-mail is confidential. If you have received this e-mail in error, please contact
> the sender and delete it from your system. All information about Personal Data
> Protection can be found on the website www.cam.es , in the Legal Disclaimer section
>
>
> ------------------------------
>
> [image: IDUG - The Worldwide DB2 User Community! ] < http://www.idug.org/db2-north-america-conference/index.html >
>
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> not already an IDUG member, please register here. < http://www.idug.org/register >
>



--
Robert Catterall
Catterall Consulting
www.catterallconsulting.com

_____________________________________________________________________

* IDUG North America * Tampa, Florida, * May 10-14 2010 * http://IDUG.ORG/NA *
_____________________________________________________________________

http://www.IDUG.org membership is now free.
Do you have people in your office who are not an IDUG member?
Show them how to access the information and help train the next generation of DB2 Users!
_____________________________________________________________________

If you need to change settings, http://www.idug.org/cgi-bin/wa?A0=DB2-L is the home of IDUG's DB2-L