Data Guard

Oracle Data Guard

Ensuring Disaster Recovery for Enterprise Data

Wei Hu

[email protected]

Oracle\u2019s High Availability (HA) Solution Stack System Failure Unplanned Downtime

Data Failure & Disaster Human Error

Planned Downtime

System Maintenance Data Maintenance

Real Application Clusters

Continuous Availability for all Applications

Data Guard Zero Data Loss

Flashback Query

Enable Users to Correct their Mistakes

Dynamic Reconfiguration

Capacity on Demand without Interruption

Online Redefinition Adapt to Change Online

Oracle Data Guard Focus \ u e 0 0 0

Data Failures & Site Disasters:

\ u 2 0 1 3

Data Protection

\ u 2 0 1 3

Data Availability

\ u 2 0 1 3

Data Recovery

All 3 are important!

Data is the core asset of the enterprise!

\ u 2 0 2 2 Also addresses human errors & planned maintena

What Is Oracle Data Guard? Database software infrastructure that automates creation and maintenance of a duplicate, or standby copy, of the production (or primary) database If the primary database becomes unavailable (disasters, maintenance), the standby database can be activated and can take over the data serving needs of the enterprise

Data Guard Architecture Overview Clients

Clients

Primary Site

Standby Site

Data Changes t n e g A r e k o r B

Primary Database

Data Guard Broker

Standby Database

t n e g A r e k o r B

How Does It Work? As primary database is modified, redo data is propagated to standby databases Standby databases kept synchronized with primary Primary database is open and active; standby database is either in recovery or open read-only / read-write

Standby database can be transitioned to the prima role as necessary

Data Guard Configuration Standby Site A

Primary Site

Sta Standby Database Primary Database

Managed as a single configuration

Standby Database

Primary and standby databases can be Real Appli or single-instance Oracle

Oracle Data Guard Architecture

Production Database

Physical Standby Database

Sync or Async Redo Shipping

Backup Redo Apply

Network

DIGITAL DATA STORAGE


Broker Optional Delay

Transform Redo to SQL

Optional Delay

Logical Standby Database

SQL Apply

Open for Reports

Additional Indexes & MVs

Oracle Data Guard Process Architecture Physical/Logical Standby Database

Oracle Net

Transactions

LGWR

(Synchronous/Asynchronous)

Online Redo Logs

FAL

Primary Database

RFS

Affirm/ NoAffirm

Standby Redo Logs

ARCH

ARCH

MRP/ LSP

Backup / Reports Transform Redo to SQL for SQL Apply

(Synchronous)

Archived Redo Logs

Archived Redo Logs

Data Guard Redo Apply Data Guard Broker Primary Database


Optional Delay

Backup

Network Sync or Async Redo Shipping


Redo Apply

Physical Standby Database is a block-for-block copy of the primary database Uses the database recovery functionality to apply changes Can be opened in read-only mode for reporting/queries Can also perform backup, offloading production database

Data Guard SQL Apply Data Guard Broker

Primary Database

Optional Delay

Additional Indexes & Materialized Views


Continuously Open for Reports

Network Sync or Async Redo Shipping

Transform Redo to SQL and Apply

Logical Standby Database is an open, independent, active database Contains the same logical information (rows) as the production database Physical organization and structure can be very different Can host multiple schemas

Can be queried for reports while logs are being applied via SQL

Can create additional indexes and materialized views for better query performan

Standby Databases Are Not Idle Standby Server

Read-Only / Read-Write Reporting

Standby Database

Tape

Backups

Standby database can be used to offload the primary database, increasing the ROI

Cascaded Redo Log Destinations Standby database receives its redo data from another standby database and not from the original primary database Primary database sends a set of redo data to only selected standby databases and not to all standby databases Reduces the load on the primary system, and also reduces network traffic and use of valuable network resources around the primary site

Primary Database

Redo Data


Retransmitted


Protection from Human Errors and Data Corruptions Standby Site

Primary Site

Standby Database

Production Database Optional Delayed Apply

The application of changes received from the primary can be delayed at standby to allow for the detection of user errors and prevent standby to be affected The apply process also revalidates the log records to prevent application of any log corruptions

Switchover and Failover Primary and Standby role transitions Switchover –

Planned role reversal

–

No database reinstantiation required

–

Used for maintenance of OS or hardware

Failover –

Unplanned failure (e.g. disasters) of primary

–

Primary database must be reinstantiated

Initiated using simple SQL / GUI interface

Data Guard automates the processes involved

Failover Example

Flexible Data Protection Modes Protection Mode

Risk of Data Loss

Maximum Protection

Zero Data Loss

Redo Shipment

Synchronous redo Double Failure Protection shipping to 2 sites

Maximum Availability

Zero Data Loss

Synchronous redo shipping Single Failure Protection

Maximum Performance

Minimal data loss – Asynchronous redo usually 0 to few seconds shipping

Balance cost, availability, performance, and transaction protection

Maximum Protection Mode Protection Mode

Risk of Data Loss

Maximum Protection

Zero Data Loss

Redo Shipment

Synchronous redo Double Failure Protection shipping to 2 sites

Highest level of data protection Configuration: LGWR SYNC, SRLs Enforces protection of every transaction If last standby is unavailable, processing stops at primary Good for financial systems where no data loss is acceptable

ALTER DATABASE SET STANDBY

TO MAXIMIZE PROTECTION;

Maximum Availability Mode Protection Mode

Risk of Data Loss

Redo Shipment

Maximum Availability

Zero Data Loss

Synchronous redo shipping

Single Failure Protection

Enforces protection of every transaction Configuration: LGWR SYNC, do not need SRLs If last standby is unavailable, processing continues at primary When the standby becomes available again, synchronization with the primary is automatic ALTER DATABASE SET STANDBY

TO MAXIMIZE AVAILABILITY;

Maximum Performance Mode Protection Mode Maximum Performance

Risk of Data Loss

Redo Shipment

Minimal data loss – Asynchronous redo usually 0 to few seconds shipping

Highest level of performance Configuration: LGWR ASYNC, or ARCH Protects from failure of any single component Least impact on production system Useful for applications that can tolerate some data loss ALTER DATABASE SET STANDBY

TO MAXIMIZE PERFORMANCE;

Automatic Gap Resolution & Resynchronization

Network connectivity problems may cause ga the sequence of log files in the standby

Data Guard automatically takes care of thes –

Automatic Gap Handling

–

FAL (Fetch Archive Log) Gap Handling

GAP Resolution Automatic –

ARCH process idling away on the primary ‘pings’ all enabled standbys on a regular basis to see if they are missing any redo data

–

If so it sends them the missing redo data

FAL –

Gap discovered during apply process in physical standby

–

Based on FAL_SERVER and FAL_CLIENT settings, primary notified, and it sends missing redo data

Oracle Data Guard Broker Distributed management framework that automates and centralizes the creation, maintenance, and monitoring of Data Guard configurations Management operations can be performed locally remotely through the Broker's easy-to-use interfaces: –

GUI-based Oracle Data Guard Manager

–

Data Guard command-line interface

Data Guard Broker Architecture Job Service

Event Service

Security Service

Discovery Service

Oracle Management Server Data Guard Manager OEM Agent

Primary Database

Data Guard Broker

OEM Agent

Data Guard Broker


OEM Agent

Data Guard Broker

Repository


Data Guard Manager

Simple, easy-to-use management and monitoring interface

Local and Remote Standby Databases Oracle Data Guard configuration can support both local remote standby databases Local standby database – – – –

Human error and data corruption protection Appropriate for highest data protection modes LAN links are cheap, reliable, have high bandwidth and low latency Switchover operations are very fast

Remote standby database – – –

Best solution for disaster recovery WAN links are generally more expensive, less reliable, have lower bandwidth and higher latency than LAN links Suitable for highest performance asynchronous data protection mode

Usage Examples Chicago

Primary Database

Standby Database

Example B

Dallas

Standby Database

Primary Database

Maximize primary and standby resources

Example A

Standby machine must be powerful enough to support multiple production instances after switchover / failover

Primary Site A

Primary Database

Primary Site B

Primary Database

Primary Site C

Primary Database

Standby Database

Standby Database

Standby Database

Standby Site

Usage Examples Primary Site

Standby Site A Synchronous transport

LAN attached Used to offload backups First choice for switchover candidate

Standby Database

Standby Site B

Primary Database

Synchronous transport LAN attached Used to offload reporting Standby Database

Example C

Standby Site C

Asynchronous transport WAN attached Delayed apply Provides DR and data protection

Standby Database

Data Guard and RAC Data Guard and Real Application Clusters are complementary should be used together for a Maximum Availability Architecture Real Application Clusters provides high availability – –

Provides rapid and automatic recovery from node failures or an instance crash Provides increased scalability

Data Guard provides disaster protection and prevents data los –

By maintaining transactionally consistent copies of primary database

–

Protects against disasters, data corruption and user errors

–

Does not require expensive and complex HW/SW mirroring

Data Guard and Streams Streams and Data Guard are independent features of Oracle Database Enterprise Edition, based on some common underlying technology Data Guard: Disaster Recovery & Data Protection – – – –

Transactionally consistent standby databases Zero data loss Automated switchover/failover Various data protection modes

Streams: Information Sharing/Distribution – – – –

Fine granularity and control over what is replicated Bi-directional replication Data transformations Heterogeneous platforms

Because of business requirements, customers may choose to use Streams for DR/HA, and Data Guard SQL Apply for information distribution

Financial Services Company Using Data Guard & Streams

Master Database

Streams

for information distribution

Data Feed

Data Guard

Data Transformation

for DR

Product Delivery Databases for Client Access


Data Guard and Remote Mirroring Remote Mirroring is another way to protect enterprise data Host-based and storage based Is a physical bit-for-bit copy The copy can be remote

Is this a good substitute?

Data Guard and Remote Mirroring Better protection –

Redo is validated logically

Greater efficiency –

Only redo is transferred instead of entire disk block (7x bandwidth savings, 27x network I/Os)

Cheaper –

No reliance on specialized hardware

Remote mirroring is useful for non-Oracle data

Why Oracle Data Guard? 1.

Disaster Recovery & High Availability –

2.

Complete data protection –

3.

Flexible data protection/synchronization modes

Automatic resynchronization after restoration of network connectivity –

6.

Standby databases can be used for reporting, backups, queries

Balance data availability against performance –

5.

Enables zero data loss, safeguard against data corruptions

Efficient utilization of system resources –

4.

Easy failover/switchover between primary and standby databases

Automatic archive gap detection and resolution with no manual intervention

Centralized and simple management –

Graphical interface for management and monitoring

Resources HA Portal on OTN: http://otn.oracle.com/deploy/availability/ Maximum Availability Architecture (best practice recommendations on Data Guard + RAC configuration): http://otn.oracle.com/deploy/availability/htdocs/maa.htm

Disaster Recovery page on OTN:

http://otn.oracle.com/deploy/availability/htdocs/dr_overview.html

Data Guard Technical White Paper on OTN: http://otn.oracle.com/deploy/availability/pdf/DG92_TWP.pdf

Data Guard Technology Overview Presentation on OTN:

http://otn.oracle.com/deploy/availability/pdf/DataGuardTechnologyOverview.pdf

Data Guard

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