special challenges drj sep 2002

8/11/2019 Special Challenges DRJ Sep 2002

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Tom Flesher

E-Net Corporation

Mainframe Database

Replication and RecoveryOver Extended Distances:

Special Challenges and

Industry Trends

Breakout Session 3

Monday, September 9, 2002

4:15 pm5:15 pm
http://www.drj.com/conferences/orl2002/24pg/http://www.drj.com/conferences/orl2002/24pg/


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Why replicate critical databases

over extended distance?

Simple answer: to have a hot standby copy of your

organizations most critical data at a remote location

in case you need it.

Business continuity your primary copy of the data is knocked out or is unavailable

for an unacceptable length of timein other words, an

unscheduled outage

Continuous availability

your primary copy will be unavailable due to a planned and

deliberate event, such as maintenance, migrations or

reorganizations

Workload balancing

you can run data mining applications against the replica copy

and avoid the overhead on the primary copy


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Demands on Your Data

CALL

CENTER

Production

DBMS

EDI

OLTP

INTERNET

DIAL-IN


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Benefits of Extended

Distance Replication

Production

Database

Replica

Database

Business Continuity

Not compromised by

regional outage

Availability Switch to backup site

during scheduled

outages

Application-driven

Ad hoc queries

Warehousing

Data mining


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A Supervisory Perspective on Disaster Recovery and Business Continuity

September 11 may lead to changes in institutions' planning for emergencies, as well as

changes in their ongoing operations. In addition to a range of tactical steps, such as

enhancing security measures, updating communication plans, and strengthening real-

time data backup, institutions also are making some interesting strategic choices..some institutions are now moving toward a "split operations" model, in which two or

more active operating sites provide backup for one another. Each site can absorb some or

all of the work of another for an extended time. For banking organizations with

nationwide operations (particularly those that have grown through mergers), such sites are

often hundreds of miles apart..Financial institutions clearly are reassessing therange of scenarios they need to address in their business-continuity planning. Such

scenarios posit effects on business operations over much broader geographic areas

than previously imagined(such as a city or a metropolitan area) and involveconsequences that could harm or significantly disperse an organization's critical

employees.

Remarks by Fed Vice Chairman Roger W. Ferguson, Jr.

to the Institute of International Bankers, Washington, D.C.

March 4, 2002

Source: Federal Reserve website

http://www.federalreserve.gov/boarddocs/speeches/2002/20020304/default.htm


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Data

Loss

(RPO)0

1 Day

1 Hour

1 Second

Recovery Time (RTO)

0 15 Minutes 6-24 Hours1-2 Hours

RPO and RTO

Technology Alternatives

Daily Backups

CTAM / Vaulting

Traditional

Journaling (and/or

Vaulting) Solutions

Asynchronous Disk Mirroring

Synchronous Disk Mirroring

(short distance only)

Asynchronous Database Replication


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Using mirrored disks for

replication

Mirroring assumes a system restart at takeover time All database files, logs, catalogs must be mirrored faithfully

Notion of time-consistent restart state simulation of thelocal/production site environment at a precise point in time

Enables database management systems to perform warmrestart processbackout of inflight transactions (ACID) andcleanup of dirty pages (e.g. Aries/DB2) - to restore databaseto a consistent state

After warm restart, data is ready to be used for applicationtakeover

Point-in-time copies can be spun off when needed For recovery testing

To support read-only applications

To freeze the entire environment while a new full copy is

being transmitted


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Refresh vs. Change Propagation

A Refreshinvolves a full copy of all data

Time-consuming

Needs lots of bandwidth

Required for all replication solutions Some permit tape / CTAM refresh..

Potential impact on production application

Change propagationinvolves capture and

transmission of changes Physical (track) vs. logical (record)

Bandwidth considerations

Synchronous and asynchronous components


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Track/Page vs Record/Row


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Challenges over Extended

Distance

Propagation Delay A fully asynchronous solution should have adequate

buffering and recovery capabilities to run over any distance

Satellite links have huge propagation delays, yet typically

very high bandwidth! Bandwidth

How many bits must move across the network over time?

Include refresh in addition to change propagation needs

Time to re-sync in event of extended network outage Just changed data or all data?

Cost Pure hardware cost, count extra copies!

Recurring network costsstill high over extended distance

Administration and maintenance costs


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Mirroring and Software-based Replication

Over Extended DistanceMajor Categories

Disk mirroring asynchronously with host data

mover

Disk mirror asynchronouslyno host

component

Software-based replication and change

propagation using logs

Software-based replication and changepropagation using middleware


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Asynchronous mirroring using

host data mover


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Asynchronous mirroring - disk

subsystem-to-subsystem


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Database log

Log has after-images of

changed records

Sometimes only changed

fields or columns Used for forward/backward

recovery processes

Concise basis for change

propagation Can be used for recovery or

replication


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Replication using logs for change

propagation


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Replication using middleware for

change propagationuni-directional


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Replication using middleware for

change propagation- bi-directional


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New York Node

West Coast Node Central Node

3-Node Replication

Uni-directional

A

A B

C

C

B

D E

F

D

E

F


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Multiple Replicas

Production Site

Backup Site #1 Backup Site #2


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Trend: multi-master

New York Node

West Coast Node Central Node

Multiple copies of the same

database

Application designed to

tolerate integrity fuzziness

Traditional ACID qualities

are compromised


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For further information please contact:

Tom Flesher

E-Net Corporation

[email protected]

Tel +1-415-835-8419Fax +1-413-332-7891

Please fill out an evaluation form.

And THANKS for attending!

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