Oracle E-BusinessAvailability Options

Solution Series for Oracle: 2 of 5

Table of Contents

Coping with E-Business Hours – Oracle E-Business Availability Options . . . . .1

Understanding Challenges to Availability . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Components of E-Business . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Dimensions of Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

A Spectrum of Availability Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

The Essentials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Approaching Continuous Availability for E-Business . . . . . . . . . . . . . . . . . .6

Replication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Oracle Automated Standby Database . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

VERITAS Volume Replicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

Volume Replicator and Oracle Automated Standby Server: A Hybrid Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Clustering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

VERITAS Cluster Server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Oracle Parallel Server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Coping with E-Business Hours – Oracle E-Business Availability Options

The world of e-business knows no business hours and has little tolerancefor failures. Site outages can lead not only to loss of income, but also tothe erosion of online brand and, in some cases, market capitalization. And as the internet economy matures, users are less forgiving, expectingconstant availability and performance and switching quickly to otherchannels or competitors if things go wrong.

This is why systems availability is a top concern among e-business companiesand also why a whole host of vendors are pushing their solutions for solvingavailability problems. However, the confusing claims and perspectives ofthese vendors can make it difficult to sort out what you need and why.

This brochure provides a broader understanding of availability as it relates tomost e-businesses and discusses some of the technologies used to achieveavailability at a high level. Many sources are available for further information.The Oracle and VERITAS Web sites both provide good starting points.

VERITAS Software has long built its business on providing Business WithoutInterruption™ for Fortune 500 companies – and now for leading e-businesses.VERITAS Software has strong partnerships with the major leading systemand storage vendors and participates with Oracle and Sun Microsystems in a strategic alliance to support e-business growth. As a leader in thestorage management industry, VERITAS Software is focused on creatingheterogeneous, scalable and manageable solutions for improving e-businessavailability in a wide variety of configurations.

VERITAS Software’s integrated suite of storage management solutionsenhances availability at all levels for e-businesses, supporting the complex,multitiered and heterogeneous platforms driving many e-business architectures.

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Understanding Challenges to Availability

One challenge in discussing high availability is that the term has differentmeanings to different audiences. A hardware vendor may talk about meantime between failures, a system administrator is interested in system faults,and a database administrator measures database availability.

Of course, the most important measure of availability for e-business isfrom the customers’ perspective. Can they perform they tasks they needto, when they need to? In this environment, a problem can lead not onlyto inconvenience, but to lost customers and a degraded online brand. Thismakes availability a business-critical concern.

Components of E-Business

When considering availability, you must think of all the components of e-business – everything it takes to deliver an online service to your customers.A typical e-business relies on an array of equipment, including Web servers,application servers, back-end databases, load balancers and middle-tierapplications.

Figure 1: Example of multitiered Web-site architecture

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Oracle Oracle

DatabaseServers

Storage Access Network

Web orApplicationServers

Load Balancers

Database Access Network

Internet

Users

Databases

Client Access LAN

To control application availability, you need to consider the entire spectrumof critical systems that deliver the application to the user.

The back-end data servers in many e-businesses use Oracle databases.This tier poses special challenges, because it must serve large amounts ofdata with high performance and possibly manage updates as well. As aresult, database availability requires extra attention as a critical componentof your availability strategy.

Dimensions of Availability

When considering e-business continuity, you must be able to protect yoursite from interruption because a variety of issues. These include:

Table 1: Dimensions of availability

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Risk Availability Challenge

Network disruption Do your customers have access to your applications? Network availability is often protected through redundant routers and connections.

System fault What if a critical system fails? Any component of the e-business application should be either highly available or redundantly deployed.

Disaster recovery How safe is your e-business from localized disasters? Comprehensive disaster recovery planning is a requirement for most businesses.

System maintenance Whether loading the latest security patches to the Web server or upgrading the storage or operating system, basic administrative activities can cause system downtime that is sometimes overlooked in availability planning.

Data loss The data that runs the e-business resides on storage devices that, likeany physical device, may fail. You need to plan for those failures and protect the data.

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A Spectrum of Availability Options

Each of the dimensions of availability has a range of potential solutions –from basic best practices to advanced technologies.

• Basic measures give a baseline level of protection at a relatively lowcost. For example, database backups provide basic protection againstsystem faults. Recovering from backups alone may require hours tobring services back online.

• Advanced measures require more work and, in many cases, more equipment. A clustered configuration with failover software providesadvanced protection from system faults, with virtually uninterruptedservice, but requires more software and equipment to implement.

Between basic and advanced are often other solutions. In the case of systemfaults, these may include standby servers and other replication solutions.

The table below illustrates a range of solutions to the various dimensionsof availability:

Table 2: The availability solution spectrum

Risk Basic solution Mid-range Advanced

Network disruption Deploy redundant Deploy high-end load- equipment. balancing equipment.

System fault Maintain good Use standby servers. Implement backups and clustering with practice recoveries. automated failover.

Disaster recovery Create comprehensive Maintain disaster recovery plan geographicallyand maintain offsite distributedbackups. replicated sites.

System maintenance Choose platforms Use a third mirror Implement clusteringthat support online split to offload with manual failoveradministrative tasks. read-only production capabilities for

systems. administrative downtime.

Data loss Use mirrored or RAID Create storage configurations geographicallyto maintain data distributedavailability in case of replicated sites.device failure.

The Essentials

Even if you are focused on the high end of the availability spectrum, theavailability basics are often a critical foundation for e-business availability.For example, good backups are always critical – even if you’re replicatingdata globally.

VERITAS Software has integrated, heterogeneous storage-managementsolutions that address most of these basic measures, creating a highlyavailable foundation for e-business.

Maintaining Backups

VERITAS NetBackup™ DataCenter is a powerful enterprise data protectionsolution for UNIX, Windows NT and NetWare environments. NetBackupprovides fast, reliable and data-center-strength backup and recovery toprotect environments that span terabytes to petabytes in size. NetBackupcan protect the Web servers, file servers and application servers that driveyour site.

Databases have special backup and recovery needs. VERITAS NetBackup™

for Oracle® is the database-aware backup and recovery agent integratedwith the NetBackup product family. NetBackup for Oracle can back upOracle databases quickly while they are online and available. VERITAS’unique block level incremental backup backs up only data blocks changedsince the last backup. Parallel backup and recovery operations enablehigh-performance backups for very large databases. The result is that youcan take backups frequently and easily, ensuring that you always have agood backup on hand.

Disaster Recovery

NetBackup can create duplicate media in a standard, nonproprietary formatfor offsite storage and disaster recovery. The Vault Extension to NetBackuphelps maintain and track offsite backups.

Online system maintenance

The VERITAS Foundation Suite™ integrates VERITAS Software’s industry-leading file system and volume management solutions, creating a scalableand flexible foundation for highly available data.

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The VERITAS Foundation Suite reduces failures because of file system panics,and speeds recovery from any file system errors. Administrators can performstorage administration while systems are online and available, using centralized management interfaces across systems and site components.

VERITAS Database Edition™ for Oracle® enhances the VERITAS FoundationSuite, combining all the functionality of that product with additional sup-port specific to Oracle databases. Database administrators can defragment orresize database storage while the database is online and available.

Data Loss

The VERITAS Foundation Suite includes the highly regarded heterogeneousvolume management software, VERITAS Volume Manager™. VolumeManager lets you create “virtual” storage volumes that can survive disk or I/O bus failure, using flexible mirroring or RAID storage techniques. TheDatabase Edition for Oracle extends these capabilities to Oracle databases.

Approaching Continuous Availability for E-Business

After implementing the availability basics just described, you can consider thetechnologies and techniques used to provide nearly continuous e-businessavailability. These introduce more complexity into the administrativeenvironment, but offer enormous payoffs in terms of system availability.

The most common availability solutions for Oracle e-business include:

Replication – The process of keeping data on multiple systems synchro-nized on an ongoing basis, replication is frequently used for publishingor distributing data across geographic locations. As such, it is a keycomponent of many disaster recovery solutions.

Hot Standby – A special case of replication, a hot standby system is a separate system, typically dedicated to its standby function, ready totake over production applications in case of the failure of primary system (System Fault). The data is kept up-to-date using some kind of replication technology.

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Clustering – An availability cluster is a grouping of computers that sharestorage and have the ability to take over the processing for a system inthe cluster that fails. Clustering technologies typically protect againstSystem Fault problems. Oracle Parallel Server is a database-specific clustering solution. VERITAS Cluster Server™ delivers application-levelfailover capabilities.

Different vendors offer different perspectives on achieving these solutions– a storage vendor takes a storage-centric approach to replication, forexample, whereas Oracle handles the issue from a database level. Theresult can be a confusing array of choices. We will talk about these at afairly high level, addressing which dimension of availability they addressand what the trade-offs are for each.

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Replication

At its simplest, replication is the process of copying data from one serverto another on an ongoing, continuous basis.

Reasons for replication include:• Publishing data to multiple sites (for follow-the-sun processing,

for example)

• Creating standby systems for failover purposes

• Protecting data from local disasters by replicating it to a remote system

• Creating a system that can be used for off-host process of backups,reporting, analysis, testing, and other data-intensive activities using production data

Solutions that work for one purpose may not work well for another. Forthis discussion, we consider replication as a means of improving availability.

Replication vs. Mirroring

Data mirroring is a kind of localized replication. Mirroring is an invaluabletool for protecting data from disk errors. Mirroring technologies require highspeed and dependable connections characteristic of I/O channels. Longer-distance links offer lower speed and less reliability. Implementing simplemirroring over these links would introduce write delays on the productionsystem, impairing performance and possibly availability if the link isunavailable. This is why we turn instead to replication technologies, designedto tolerate the less reliable connections required by longer distances.

Although mirroring protects data from the loss of the storage device, replication to a remote site protects from both the loss of the storagedevice and a localized disaster.

How Replication Works

Most replication implementations are fairly simple in principle. A replicationmanager on the primary system (the source for the data) intercepts liveupdates as they occur and distributes them to one or more replicationmanagers at remote sites. Replication managers handle delays of theinterconnections by buffering the changes at the primary site if necessary.

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One distinction between replication solutions is how continuously theywrite changes between systems. Options include:

Synchronous replication – In a synchronous replication environment,data must be written to the target before the write operation completeson the host system. This assures the highest possible level of data integrityfor the target system – at any point in time, it will have the exact samedata as the source. This can introduce performance delays on the sourcesystem if the network connection between the systems is slow.

Asynchronous replication – Using asynchronous replication, the sourcesystem does not wait for a confirmation from the target systems beforeproceeding. Products may queue data and send batches of changesbetween the systems during periods of network availability. This results inbetter performance over uncertain network connections, but the targetsystem may be slightly “behind” the source; the replication managermust log changes on each end carefully.

Scheduled replication – For some purposes, it may be preferable touse scheduled, delayed or periodic replication, in which changed data issynchronized at predefined intervals or on an ad hoc basis. This is usefulin some data publication or off-host processing implementations.

There are several different approaches to replication for disaster recoverypurposes; Oracle Standby Server uses a database-level approach to replication; VERITAS Volume Replicator™ replicates data at the logicalvolume level.

Oracle Automated Standby Database

The Oracle Automated Standby Database uses archived redo logs to writechanges from a source database (the “master database”) to one or morereplicated servers. If one or more of the replicated servers resides in a different physical location, it can serve as a disaster-recovery solution.

After initially copying the production database to the standby server,Automated Standby Server keeps the standby system up-to-date by copyingand recovering the production system’s transactions (in the archived redologs) to the standby system.

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The replicated site is normally in a sustained recovery mode (it is alwaysloading redo logs). You can also put this database in a read-only state toperform reporting, decision support or other query-intensive work. Duringthis phase, the archived redo logs are not loaded from the master; theDBA must restore the database to its recovery state to continue.

In the event of a failure, simply redirecting application queries to thestandby database serves as a relatively fast response to system problems.

VERITAS Volume Replicator

VERITAS Volume Replicator is a highly scalable and flexible solution formanaging ongoing data replication to one or more sites, with guaranteeddata integrity. Implemented as a VERITAS Volume Manager module,Volume Replicator replicates data at the logical volume level.

Replication is completely transparent to database application (or any otherapplications). Whenever data is written to the replicated volume, VolumeReplicator automatically sends it to one or more sites (depending on theconfiguration).

Key points about Automated Standby Server

It is noninvasive, with low overhead on the production system.

This approach works best for a single instance. Within this framework, it is flexible; you canchoose to replicate only specific tables in the database.

The network must have sufficient bandwidth to handle the transfer of archive logs, which can be significant in databases with heavy transaction volumes.

The replicated site should be as close as possible in terms of hardware/software configuration to the production site.

This approach creates a kind of scheduled/delayed replication, because changes aren’t written tothe standby server until the redo log is archived. You can also add a scheduled delay, so that you can catch data corruption before replicating it.

Recovery on the replicated site requires some effort on the part of the DBA – the most recentredo logs on the production database must be transferred to the replicated site and loaded there.Otherwise, the replicated site will have updates only to the point of the last archived redo log.

Figure 2: Volume Replicator replicates data between sites over an IP link. Only logical volumes are replicated – not necessarily the entire site.

Volume Replicator performs both synchronous and asynchronous replication.Using synchronous replication, the initial write is not committed until thedata has been replicated successfully. With asynchronous replication, repli-cation operations queue for network availability. Asynchronous replicationprovides the highest performance. In a “soft synchronous” mode, replicationis synchronous under normal circumstances, but converts to asynchronousin the case of a temporary network outage. In all cases, replication is anongoing, constant, and transparent activity.

VERITAS Volume Replicator supports a variety of replication configurations,including one-to-one, one-to-many, and many-to-one.

Operating at the logical volume level has some distinct advantages.Although it requires a dedicated volume on the replicated system, it doesnot require that the entire system be dedicated to its replication function.So it is possible to create a configuration like the one in Figure 3, in whichtwo sites act as reciprocal disaster recovery sites for each other:

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IP NETWORK

SITE 1

VOLUMEMANAGERVOLUME

MANAGER

VOLUMEREPLICATOR

127-GBVolume

500-GBVolume

50-GBVolume

LOGLOG

ReplicatedVolumeGroup

R-LINK

SITE 2

APPLICATION

FILE SYSTEM

VOLUMEMANAGER

APPLICATION

FILE SYSTEM

VOLUMEMANAGER

VOLUMEREPLICATOR

127-GBVolume

500-GBVolume

50-GBVolume

ReplicatedVolume

Group

AC

TIV

EI/

O

FILE SYSTEMFILE SYSTEM

APPLICATIONAPPLICATION

R-LINK

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Figure 3: A reciprocal disaster recovery configuration using VERITAS Volume Replicator.

Volume Replicator and Oracle Automated Standby Server: A Hybrid Approach

A third approach to Oracle replication combines the two mentionedabove. Using Volume Replicator, you can replicate the master server’sonline redo logs to the disaster recovery site. This means that you canbring the standby server up-to-the-minute very quickly – without havingto retrieve the online redo logs from the production server.

This hybrid solution has been tested in Oracle Corporation’s Oracle StorageCompatibility Program (OSCP) and approved by Oracle for up-to-date disaster recovery of Oracle databases.

Key points about VERITAS Volume Replicator

Replication occurs at the logical volume level – it is transparent to the software and configurationis flexible. It also supports any data type, including databases stored on raw partitions.

Volume Replicator works over any IP network, LAN or WAN, supporting up to 32 nodes in a replicated network.

Volume Replicator ensures the integrity of data on all systems, all the time, by carefully maintaining write order consistency when writing replicated data.

Volume Replicator can use a combination of asynchronous and synchronous replication – delaying replication when the connection is unavailable or slow and reverting to synchronousreplication when the connection clears.

Volume Replicator does not require that the systems have identical configurations.

App B1App A2

App Areplica

App BvolumeApp A

1App B2

App Breplica

App Avolume

App Bupdates

App Aupdates

Clustering

Clustering is an important technology for both availability and performancescalability concerns. The basic idea behind clustering is to have a groupingof loosely connected systems (nodes in the cluster) that can perform thesame task. If one fails, another takes over. If you need to handle morerequests, you can simply add another node.

At its simplest, a cluster has two or more nodes that are interconnected(with redundant connections). The nodes must share access to clients andto storage.

The shared storage access is most frequently implemented with a storagearea network (SAN) using fibre channel technology. This is a highly scalableand flexible storage configuration. A cluster may in fact be a fairly simpleimplementation of two servers sharing a switched SCSI device.

Figure 4: A simple cluster configuration

The cluster also requires cluster software that monitors the availability ofthe servers or the applications and network connections and transfers anapplication to another server in the case of a failure on a node.

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Oracle Oracle Oracle

LANCommon Client Access

SANCommon Data Access

Access to data

One way to define clusters is by how they share access to the data.

• The simplest kind of cluster to implement is a shared nothing cluster.Although the nodes in the cluster can access a common set of data, onlyone cluster “owns” the data at one time. If that node fails, ownershippasses to another node that can then access the data.

• In a shared data cluster, different nodes of the cluster can access and potentially update the same set of data. This requires software (a distributed lock manager) that manages contention between requests,to be sure that the data remains consistent. Shared data configurationsof read-only data, such as Web pages, can be implemented using a cluster-aware file system (such as VERITAS Cluster File System™). Within a database, the database engine must perform this function.

These distinctions are important when we consider two commonapproaches to clustering for Oracle databases: shared nothing availabilityclusters (with a product such as VERITAS Cluster Server) and shared datascalability clusters (with Oracle Parallel Server).

VERITAS Cluster Server

VERITAS Cluster Server (VCS) is the VERITAS Software solution for application-level availability clusters. Using VCS, you can create easy-to-manage, flexibleclusters that protect critical applications in clusters of up to 32 nodes.

VCS software takes an application-level approach to managing clusters.Application processes, their network interfaces and storage resources aregrouped as interdependent resources, all under VCS control. This series ofresources is referred to as a resource group and can be migrated as a wholeto other nodes within the cluster to provide application availability to clients.

For example, an application referencing an Oracle database requires theOracle instance, the database, the storage devices on which the databaseresides, and the network card and IP address used to communicate withclients. If VCS has to fail over the application to another server, it migratesall the resources required for the application to the new node.

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VCS uses application-specific agents to monitor the various resources. Forexample, VERITAS has created Oracle-specific VCS agents. All failover ispolicy based; you can define the potential restart or failover activities. AndVCS can support multiple node failures with cascading failover.

Oracle Parallel Server

Oracle Parallel Server (OPS) is a shared data clustering application. It addsboth availability and scalability, because you can have multiple serverinstances accessing the same shared database – something only possiblewith the distributed lock management capabilities of OPS.

Oracle Parallel Server has been available for many years. The Oracle8irelease has brought many enhancements, including cluster load balancingand improved system manageability. Cache management technology(Cache Fusion in Oracle8i ) and Oracle Parallel Query technologies helpaddress performance for distributed access to the same set of data.

Oracle Parallel Server is really the only clustering alternative for Oracle ifyou need horizontal scalability (the ability to serve more users by addingserver instances accessing the same database) for writable databases.

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Key points about VERITAS Cluster Server

The VERITAS Cluster Server implementation is transparent to the Oracle instance – you do notneed to make any database or application changes to run in the VCS environment.

The nodes do not share access to the same Oracle database. However, if the data is read-only,they can each access copies of the same read-only database, providing scalability of the site as a whole for processing read-only requests.

VCS takes an application-level view of availability, rather than focusing exclusively on the database and database instance. This is often useful in multitiered application environments.

VCS clusters are relatively easy to manage and maintain. VERITAS also makes the Global ClusterManager™ solution that monitors multiple, geographically distributed Solaris-based VCS clustersand can fail over between clusters. This allows a global view of availability.

VCS has manual failover capabilities for administrative purposes, which can protect against outages for administrative purposes (the system maintenance availability dimension).

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The VERITAS and Oracle approaches are inherently complementary; anOracle database could run on a shared volume or within a clustered filesystem and be protected by VERITAS Cluster Server. Future versions ofVERITAS Cluster Server will support OPS configurations as part of a comprehensive approach to highly available systems.

Key points about Oracle Parallel Server

OPS manages availability at the database and database instance level.

OPS can support up to eight servers accessing a single database.

Even if a single node of the OPS cluster fails, the database remains up, eliminating time-consuming database recovery processes for system failures.

OPS provides horizontal scalability as well as availability – you can add nodes to an application accessing the same database.

For optimum performance, you need to design your application to work with OPS.

OPS environment has different administrative issues than a standard Oracle installation andrequires database administrators with OPS knowledge.

Summary

If you’re in e-business, you need nearly nonstop availability of your siteand core systems. Achieving high availability is a complex undertaking – in part because there are so many dimensions of availability or kinds offailures to protect against.

It is important to build on a strong foundation of high-performance, highlyavailable platforms combined with best practices for disaster recovery anddata recovery. Once you have done that, replication can offer protectionfrom system fault, data loss and localized disasters, while clustering withfailover can protect your business from system fault and system mainte-nance downtime.

Whether you use one or both of these approaches to availability, VERITASSoftware has integrated storage management solutions that can help.Working in close cooperation with Oracle Corporation, VERITAS ensuresthat its solutions can handle the most demanding Oracle installations. And because it supports a wide range of heterogeneous systems withavailability, clustering and replication purposes, it can protect the entiree-business architecture.

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VERITAS Software CorporationCorporate Headquarters1600 Plymouth StreetMountain View, CA 94043650-527-8000 or 800-327-2232

For additional information about VERITAS Software, itsproducts, or the location of an office near you, pleasecall our corporate headquarters or visit our Web site atwww.veritas.com

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Copyright © 2001 VERITAS Software. All Rights Reserved. VERITAS, VERITAS SOFTWARE,the VERITAS logo, Business Without Interruption, VERITAS The Data Availability Company,VERITAS Database Edition, VERITAS Cluster File System, VERITAS Volume Manager, VERITASGlobal Cluster Manager, VERITAS NetBackup, VERITAS Cluster Server, VERITAS FoundationSuite, and VERITAS Volume Replicator are trademarks of VERITAS Software Corporationin the US and other countries. Other product names mentioned herein may be trademarksand/or registered trademarks of their respective companies. Printed in USA. January 2001.