CF questions when recovering a db2 sysplex setup at DR

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CF questions when recovering a db2 sysplex setup at DR
HI all

We are about to mirror just dasd from our prod site to our dr site... How
is a DB2 recover handled when pages in the coupling facility are not at
the dr site.

Tom



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Douwe van Sluis

Re: CF questions when recovering a db2 sysplex setup at DR
(in response to ttaylor@CHUBB.COM)
Tom,

This IS handled by DB2 ;-).
It would be to much to explain by mail how exactly everything works in
detail. So take a look in the DB2 documentation about Datasharing
Recovery.
- SG24-7322 - DB2 Datasharing in a Nutshell
- SG24-4791 - DB2 V4 Data Sharing Implementation (old, but most info
still holds)
- SG24-6370 - Disaster Recovery with DB2 for z/OS (Chapter 21)
- DB2 Manual "Datasharing Planning and Administration.
- And don't forget the DB2 Information Center
http://publib.boulder.ibm.com/infocenter/dzichelp/v2r2/topic/com.ibm.db2
.doc.dshare/bjnzspsh.htm

In short. There are no dirty pages in the Group Bufferpool. All pages in
the GBP are in some form on disk. Hopefully as a page in a space on
disk, or minimal as logrecords on the DB2 Log on Disk. So there are no
pages in the GBP that are in-memory only. DB2 keeps track of pages not
yet externalized to disk and in case of a failure will set LPL for those
pages. At DB2 startup, DB2 will try to recover these pages back from the
log.



Vriendelijke groet,
Douwe van Sluis


-----Oorspronkelijk bericht-----
Van: DB2 Data Base Discussion List [mailto:[login to unmask email] Namens
[login to unmask email]
Verzonden: woensdag 10 december 2008 14:41
Aan: [login to unmask email]
Onderwerp: [DB2-L] CF questions when recovering a db2 sysplex setup at
DR



HI all

We are about to mirror just dasd from our prod site to our dr site...
How is a DB2 recover handled when pages in the coupling facility are not
at the dr site.

Tom




_____


< http://idug.org/lsNA > IDUG 2009 - North America * May 11-15, 2009 *
Denver, CO, USA

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______________________________________________________________________

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______________________________________________________________________



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Robert Catterall

Re: CF questions when recovering a db2 sysplex setup at DR
(in response to Douwe van Sluis)
I'd say that there are dirty pages in the GBP, just as there are dirty pages
in DB2 buffer pools in a non-data sharing environment (or in a data sharing
environment for page sets that aren't group buffer pool dependent). What we
mean by "dirty" is "updated but not yet written to the associated page set
on disk." Having the corresponding data changes recorded in the log doesn't
mean that the pages aren't dirty - it just means that DB2 can perform the
necessary actions upon restart to get the database objects on disk
(tablespaces and indexes) in a consistent state.

In a disaster recovery situation, at the DR site (with remote mirrored disk
mirroring in operation) the page sets that were group buffer pool dependent
at the time of the primary site disaster event would be placed in GRECP
(group buffer pool recover pending) status. In addition to having objects
placed in GRECP status, during restart DB2 could also put some pages, or
ranges of pages, on the LPL (logical page list).

Note: when GRECP and LPL conditions are detected and set by DB2 during
restart, they are not automatically cleared by DB2. You have to manually
initiate recovery via -START DATABASE commands (if for some reason -START
DATABASE is not able to clear GRECP/LPL status for an object, this can be
accomplished via the RECOVER utility).

It was mentioned that "just DASD" will be mirrored at the DR site. In fact,
this is the norm. Mirroring the coupling facilities would not be feasible
over a distance greater than a few thousand feet, as propagation delay would
negatively impact system performance in a major way. You can successfully
mirror disk volumes synchronously over a distance of 20 miles or so because
adding a few hundred microseconds to a disk I/O write response time that
would normally be a couple of thousand microseconds anyway is generally not
a big deal (for the round-trip delay due to time on the fiber link, just
start with the fact that light travels 186,000 miles per second, and do the
math based on the there-and-back distance covered). On the other hand,
adding 200-300 microseconds to a coupling facility request normally serviced
in a few 10s of microseconds, and doing that a thousand or more times per
second, would be very bad for performance. You'd be elongating coupling
facility request service times by an order of magnitude or more. So, mirror
your disk volumes, and be prepared to do GRECP/LPL recovery in the event of
a disaster. The two more recently published IBM "red books" cited (*DB2
Data Sharing in a Nutshell *and *Disaster Recovery with DB2 for z/OS*)
provide some very useful tips with respect to simplifying and optimizing the
performance of manual GRECP/LPL recovery.

Robert


On Wed, Dec 10, 2008 at 9:49 AM, Douwe van Sluis <[login to unmask email]>wrote:

> Tom,
>
> This IS handled by DB2 ;-).
> It would be to much to explain by mail how exactly everything works in
> detail. So take a look in the DB2 documentation about Datasharing Recovery.
> - SG24-7322 - DB2 Datasharing in a Nutshell
> - SG24-4791 - DB2 V4 Data Sharing Implementation (old, but most info still
> holds)
> - SG24-6370 - Disaster Recovery with DB2 for z/OS (Chapter 21)
> - DB2 Manual "Datasharing Planning and Administration.
> - And don't forget the DB2 Information Center
> http://publib.boulder.ibm.com/infocenter/dzichelp/v2r2/topic/com.ibm.db2.doc.dshare/bjnzspsh.htm
>
> In short. There are no dirty pages in the Group Bufferpool. All pages in
> the GBP are in some form on disk. Hopefully as a page in a space on disk, or
> minimal as logrecords on the DB2 Log on Disk. So there are no pages in the
> GBP that are in-memory only. DB2 keeps track of pages not yet externalized
> to disk and in case of a failure will set LPL for those pages. At DB2
> startup, DB2 will try to recover these pages back from the log.
>
>
>
> *Vriendelijke groet, **
> **Douwe van Sluis**
> ** *
>
> -----Oorspronkelijk bericht-----
> *Van:* DB2 Data Base Discussion List [mailto:[login to unmask email] *Namens
> *[login to unmask email]
> *Verzonden:* woensdag 10 december 2008 14:41
> *Aan:* [login to unmask email]
> *Onderwerp:* [DB2-L] CF questions when recovering a db2 sysplex setup at
> DR
>
>
> HI all
>
> We are about to mirror *just dasd* from our prod site to our dr site...
> How is a DB2 recover handled when pages in the coupling facility are not at
> the dr site.
>
> Tom
>
>
>
> ------------------------------
>
> *IDUG 2009 - North America * May 11-15, 2009 * Denver, CO, USA * < http://idug.org/lsNA >
>
> The IDUG DB2-L Listserv is only part of your membership in IDUG. The DB2-L
> list archives, FAQ, and delivery preferences are at *IDUG.ORG < http://www.idug.org/lsidug >
> * under the Listserv tab. While at the site, you can also access the IDUG
> Online Learning Center, Tech Library and Code Place, see the latest IDUG *conference
> information < http://www.idug.org/lsconf > *, and much more. *If you have not
> yet signed up for Basic Membership in IDUG, available at no cost, click on Member
> Services < http://www.idug.org/lsms > *
>
>
> ------------------------------
>
> *IDUG 2009 - North America * May 11-15, 2009 * Denver, CO, USA * < http://idug.org/lsNA >
>
> The IDUG DB2-L Listserv is only part of your membership in IDUG. The DB2-L
> list archives, FAQ, and delivery preferences are at *IDUG.ORG < http://www.idug.org/lsidug >
> * under the Listserv tab. While at the site, you can also access the IDUG
> Online Learning Center, Tech Library and Code Place, see the latest IDUG *conference
> information < http://www.idug.org/lsconf > *, and much more. * If you have
> not yet signed up for Basic Membership in IDUG, available at no cost, click
> on Member Services < http://www.idug.org/lsms > *
>



--
Robert Catterall
Catterall Consulting
www.catterallconsulting.com

______________________________________________________________________

* IDUG 2009 Denver, CO, USA * May 11-15, 2009 * http://IDUG.ORG/lsNA *
______________________________________________________________________



The IDUG DB2-L Listserv is only part of your membership in IDUG. The DB2-L list archives, FAQ, and delivery preferences are at http://www.idug.org/lsidug under the Listserv tab. While at the site, you can also access the IDUG Online Learning Center, Tech Library and Code Place, see the latest IDUG conference information and much more. If you have not yet signed up for Basic Membership in IDUG, available at no cost, click on Member Services at http://www.idug.org/lsms