Oracle E-Business Availability 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 tolerance for failures. Site outages can lead not only to loss of income, but also to the erosion of online brand and, in some cases, market capitalization. And as the internet economy matures, users are less forgiving, expecting constant availability and performance and switching quickly to other channels or competitors if things go wrong. This is why systems availability is a top concern among e-business companies and also why a whole host of vendors are pushing their solutions for solving availability problems. However, the confusing claims and perspectives of these vendors can make it difficult to sort out what you need and why. This brochure provides a broader understanding of availability as it relates to most e-businesses and discusses some of the technologies used to achieve availability 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 Without Interruption for Fortune 500 companies and now for leading e-businesses. VERITAS Software has strong partnerships with the major leading system and storage vendors and participates with Oracle and Sun Microsystems in a strategic alliance to support e-business growth. As a leader in the storage management industry, VERITAS Software is focused on creating heterogeneous, scalable and manageable solutions for improving e-business availability in a wide variety of configurations. VERITAS Software s integrated suite of storage management solutions enhances availability at all levels for e-businesses, supporting the complex, multitiered and heterogeneous platforms driving many e-business architectures. Oracle E-Business Availability Options Page 1
Understanding Challenges to Availability One challenge in discussing high availability is that the term has different meanings to different audiences. A hardware vendor may talk about mean time 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 is from the customers perspective. Can they perform they tasks they need to, when they need to? In this environment, a problem can lead not only to inconvenience, but to lost customers and a degraded online brand. This makes 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-tier applications. Users Internet Load Balancers Client Access LAN Web or Application Servers Database Access Network Database Servers Storage Access Network Databases Oracle Oracle Figure 1: Example of multitiered Web-site architecture Page 2 www.veritas.com/oracle
To control application availability, you need to consider the entire spectrum of 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 of data with high performance and possibly manage updates as well. As a result, database availability requires extra attention as a critical component of your availability strategy. Dimensions of Availability When considering e-business continuity, you must be able to protect your site from interruption because a variety of issues. These include: Risk Network disruption System fault Disaster recovery System maintenance Data loss Availability Challenge Do your customers have access to your applications? Network availability is often protected through redundant routers and connections. What if a critical system fails? Any component of the e-business application should be either highly available or redundantly deployed. How safe is your e-business from localized disasters? Comprehensive disaster recovery planning is a requirement for most businesses. 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. The data that runs the e-business resides on storage devices that, like any physical device, may fail. You need to plan for those failures and protect the data. Table 1: Dimensions of availability Oracle E-Business Availability Options Page 3
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 low cost. For example, database backups provide basic protection against system faults. Recovering from backups alone may require hours to bring services back online. Advanced measures require more work and, in many cases, more equipment. A clustered configuration with failover software provides advanced protection from system faults, with virtually uninterrupted service, but requires more software and equipment to implement. Between basic and advanced are often other solutions. In the case of system faults, these may include standby servers and other replication solutions. The table below illustrates a range of solutions to the various dimensions of availability: Risk Basic solution Mid-range Advanced Network disruption Deploy redundant Deploy high-end loadequipment. 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 geographically and maintain offsite distributed backups. replicated sites. System maintenance Choose platforms Use a third mirror Implement clustering that support online split to offload with manual failover administrative tasks. read-only production capabilities for systems. administrative downtime. Data loss Use mirrored or RAID Create storage configurations geographically to maintain data distributed availability in case of replicated sites. device failure. Table 2: The availability solution spectrum Page 4 www.veritas.com/oracle
The Essentials Even if you are focused on the high end of the availability spectrum, the availability basics are often a critical foundation for e-business availability. For example, good backups are always critical even if you re replicating data globally. VERITAS Software has integrated, heterogeneous storage-management solutions that address most of these basic measures, creating a highly available foundation for e-business. Maintaining Backups VERITAS NetBackup DataCenter is a powerful enterprise data protection solution for UNIX, Windows NT and NetWare environments. NetBackup provides fast, reliable and data-center-strength backup and recovery to protect environments that span terabytes to petabytes in size. NetBackup can protect the Web servers, file servers and application servers that drive your site. Databases have special backup and recovery needs. VERITAS NetBackup for Oracle is the database-aware backup and recovery agent integrated with the NetBackup product family. NetBackup for Oracle can back up Oracle databases quickly while they are online and available. VERITAS unique block level incremental backup backs up only data blocks changed since the last backup. Parallel backup and recovery operations enable high-performance backups for very large databases. The result is that you can take backups frequently and easily, ensuring that you always have a good backup on hand. Disaster Recovery NetBackup can create duplicate media in a standard, nonproprietary format for offsite storage and disaster recovery. The Vault Extension to NetBackup helps maintain and track offsite backups. Online system maintenance The VERITAS Foundation Suite integrates VERITAS Software s industryleading file system and volume management solutions, creating a scalable and flexible foundation for highly available data. Oracle E-Business Availability Options Page 5
The VERITAS Foundation Suite reduces failures because of file system panics, and speeds recovery from any file system errors. Administrators can perform storage administration while systems are online and available, using centralized management interfaces across systems and site components. VERITAS Database Edition for Oracle enhances the VERITAS Foundation Suite, combining all the functionality of that product with additional support specific to Oracle databases. Database administrators can defragment or resize database storage while the database is online and available. Data Loss The VERITAS Foundation Suite includes the highly regarded heterogeneous volume management software, VERITAS Volume Manager. Volume Manager lets you create virtual storage volumes that can survive disk or I/O bus failure, using flexible mirroring or RAID storage techniques. The Database 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 the technologies and techniques used to provide nearly continuous e-business availability. These introduce more complexity into the administrative environment, 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 synchronized on an ongoing basis, replication is frequently used for publishing or distributing data across geographic locations. As such, it is a key component 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 to take 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. Page 6 www.veritas.com/oracle
Clustering An availability cluster is a grouping of computers that share storage and have the ability to take over the processing for a system in the cluster that fails. Clustering technologies typically protect against System Fault problems. Oracle Parallel Server is a database-specific clustering solution. VERITAS Cluster Server delivers application-level failover capabilities. Different vendors offer different perspectives on achieving these solutions a storage vendor takes a storage-centric approach to replication, for example, whereas Oracle handles the issue from a database level. The result can be a confusing array of choices. We will talk about these at a fairly high level, addressing which dimension of availability they address and what the trade-offs are for each. Oracle E-Business Availability Options Page 7
Replication At its simplest, replication is the process of copying data from one server to 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. For this discussion, we consider replication as a means of improving availability. Replication vs. Mirroring Data mirroring is a kind of localized replication. Mirroring is an invaluable tool for protecting data from disk errors. Mirroring technologies require high speed and dependable connections characteristic of I/O channels. Longerdistance links offer lower speed and less reliability. Implementing simple mirroring over these links would introduce write delays on the production system, impairing performance and possibly availability if the link is unavailable. This is why we turn instead to replication technologies, designed to 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 storage device and a localized disaster. How Replication Works Most replication implementations are fairly simple in principle. A replication manager on the primary system (the source for the data) intercepts live updates as they occur and distributes them to one or more replication managers at remote sites. Replication managers handle delays of the interconnections by buffering the changes at the primary site if necessary. Page 8 www.veritas.com/oracle
One distinction between replication solutions is how continuously they write changes between systems. Options include: Synchronous replication In a synchronous replication environment, data must be written to the target before the write operation completes on the host system. This assures the highest possible level of data integrity for the target system at any point in time, it will have the exact same data as the source. This can introduce performance delays on the source system if the network connection between the systems is slow. Asynchronous replication Using asynchronous replication, the source system does not wait for a confirmation from the target systems before proceeding. Products may queue data and send batches of changes between the systems during periods of network availability. This results in better performance over uncertain network connections, but the target system may be slightly behind the source; the replication manager must log changes on each end carefully. Scheduled replication For some purposes, it may be preferable to use scheduled, delayed or periodic replication, in which changed data is synchronized at predefined intervals or on an ad hoc basis. This is useful in some data publication or off-host processing implementations. There are several different approaches to replication for disaster recovery purposes; Oracle Standby Server uses a database-level approach to replication; VERITAS Volume Replicator replicates data at the logical volume level. Oracle Automated Standby Database The Oracle Automated Standby Database uses archived redo logs to write changes from a source database (the master database ) to one or more replicated 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 copying and recovering the production system s transactions (in the archived redo logs) to the standby system. Oracle E-Business Availability Options Page 9
The replicated site is normally in a sustained recovery mode (it is always loading redo logs). You can also put this database in a read-only state to perform reporting, decision support or other query-intensive work. During this phase, the archived redo logs are not loaded from the master; the DBA must restore the database to its recovery state to continue. In the event of a failure, simply redirecting application queries to the standby database serves as a relatively fast response to system problems. 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 can choose 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 to the 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 recent redo 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. VERITAS Volume Replicator VERITAS Volume Replicator is a highly scalable and flexible solution for managing ongoing data replication to one or more sites, with guaranteed data 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 other applications). Whenever data is written to the replicated volume, Volume Replicator automatically sends it to one or more sites (depending on the configuration). Page 10 www.veritas.com/oracle
SITE 1 APPLICATION FILE SYSTEM SITE 2 APPLICATION FILE SYSTEM ACTIVE I/O VOLUME MANAGER VOLUME REPLICATOR R-LINK IP NETWORK R-LINK VOLUME MANAGER VOLUME REPLICATOR 127-GB Volume 500-GB Volume LOG Replicated Volume Group Replicated Volume Group 127-GB Volume 500-GB Volume LOG 50-GB Volume 50-GB Volume 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 the data has been replicated successfully. With asynchronous replication, replication operations queue for network availability. Asynchronous replication provides the highest performance. In a soft synchronous mode, replication is synchronous under normal circumstances, but converts to asynchronous in the case of a temporary network outage. In all cases, replication is an ongoing, 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 does not 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 which two sites act as reciprocal disaster recovery sites for each other: Oracle E-Business Availability Options Page 11
App A updates App B updates App A volume App B volume App A 1 App B 2 App B replica App A replica App B 1 App A 2 Figure 3: A reciprocal disaster recovery configuration using VERITAS Volume Replicator. Key points about VERITAS Volume Replicator Replication occurs at the logical volume level it is transparent to the software and configuration is 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 synchronous replication when the connection clears. Volume Replicator does not require that the systems have identical configurations. Volume Replicator and Oracle Automated Standby Server: A Hybrid Approach A third approach to Oracle replication combines the two mentioned above. Using Volume Replicator, you can replicate the master server s online redo logs to the disaster recovery site. This means that you can bring the standby server up-to-the-minute very quickly without having to retrieve the online redo logs from the production server. This hybrid solution has been tested in Oracle Corporation s Oracle Storage Compatibility Program (OSCP) and approved by Oracle for up-to-date disaster recovery of Oracle databases. Page 12 www.veritas.com/oracle
Clustering Clustering is an important technology for both availability and performance scalability concerns. The basic idea behind clustering is to have a grouping of loosely connected systems (nodes in the cluster) that can perform the same task. If one fails, another takes over. If you need to handle more requests, 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 and to storage. The shared storage access is most frequently implemented with a storage area network (SAN) using fibre channel technology. This is a highly scalable and flexible storage configuration. A cluster may in fact be a fairly simple implementation of two servers sharing a switched SCSI device. LAN Common Client Access SAN Common Data Access Oracle Oracle Oracle Figure 4: A simple cluster configuration The cluster also requires cluster software that monitors the availability of the servers or the applications and network connections and transfers an application to another server in the case of a failure on a node. Oracle E-Business Availability Options Page 13
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, only one cluster owns the data at one time. If that node fails, ownership passes 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 configurations of 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 common approaches to clustering for Oracle databases: shared nothing availability clusters (with a product such as VERITAS Cluster Server) and shared data scalability clusters (with Oracle Parallel Server). VERITAS Cluster Server VERITAS Cluster Server (VCS) is the VERITAS Software solution for applicationlevel availability clusters. Using VCS, you can create easy-to-manage, flexible clusters 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 are grouped as interdependent resources, all under VCS control. This series of resources is referred to as a resource group and can be migrated as a whole to other nodes within the cluster to provide application availability to clients. For example, an application referencing an Oracle database requires the Oracle instance, the database, the storage devices on which the database resides, and the network card and IP address used to communicate with clients. If VCS has to fail over the application to another server, it migrates all the resources required for the application to the new node. Page 14 www.veritas.com/oracle
VCS uses application-specific agents to monitor the various resources. For example, VERITAS has created Oracle-specific VCS agents. All failover is policy based; you can define the potential restart or failover activities. And VCS can support multiple node failures with cascading failover. Key points about VERITAS Cluster Server The VERITAS Cluster Server implementation is transparent to the Oracle instance you do not need 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 Cluster Manager solution that monitors multiple, geographically distributed Solaris-based VCS clusters and 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). Oracle Parallel Server Oracle Parallel Server (OPS) is a shared data clustering application. It adds both availability and scalability, because you can have multiple server instances accessing the same shared database something only possible with the distributed lock management capabilities of OPS. Oracle Parallel Server has been available for many years. The Oracle8i release has brought many enhancements, including cluster load balancing and improved system manageability. Cache management technology (Cache Fusion in Oracle8i) and Oracle Parallel Query technologies help address performance for distributed access to the same set of data. Oracle Parallel Server is really the only clustering alternative for Oracle if you need horizontal scalability (the ability to serve more users by adding server instances accessing the same database) for writable databases. Oracle E-Business Availability Options Page 15
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 and requires database administrators with OPS knowledge. The VERITAS and Oracle approaches are inherently complementary; an Oracle database could run on a shared volume or within a clustered file system and be protected by VERITAS Cluster Server. Future versions of VERITAS Cluster Server will support OPS configurations as part of a comprehensive approach to highly available systems. Page 16 www.veritas.com/oracle
Summary If you re in e-business, you need nearly nonstop availability of your site and core systems. Achieving high availability is a complex undertaking in part because there are so many dimensions of availability or kinds of failures to protect against. It is important to build on a strong foundation of high-performance, highly available platforms combined with best practices for disaster recovery and data recovery. Once you have done that, replication can offer protection from system fault, data loss and localized disasters, while clustering with failover can protect your business from system fault and system maintenance downtime. Whether you use one or both of these approaches to availability, VERITAS Software has integrated storage management solutions that can help. Working in close cooperation with Oracle Corporation, VERITAS ensures that its solutions can handle the most demanding Oracle installations. And because it supports a wide range of heterogeneous systems with availability, clustering and replication purposes, it can protect the entire e-business architecture. Oracle E-Business Availability Options Page 17
VERITAS Software Corporation Corporate Headquarters 1600 Plymouth Street Mountain View, CA 94043 650-527-8000 or 800-327-2232 For additional information about VERITAS Software, its products, or the location of an office near you, please call our corporate headquarters or visit our Web site at www.veritas.com 90-00561-399 VER10-ORAAOB-0000 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, VERITAS Global Cluster Manager, VERITAS NetBackup, VERITAS Cluster Server, VERITAS Foundation Suite, and VERITAS Volume Replicator are trademarks of VERITAS Software Corporation in the US and other countries. Other product names mentioned herein may be trademarks and/or registered trademarks of their respective companies. Printed in USA. January 2001.