High Availability Solutions
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Availability is the degree to which an application or service is available when and with the functionality, users expect. Availability is measured by the perception of an application's end user. End users experience frustration when their data is unavailable, and they do not understand or care to differentiate between the complex components of an overall solution. Performance failures due to higher than expected usage create the same havoc as the failure of critical components in the solution. Reliability, recoverability and continuous operations are three characteristics of a highly available solution: We can deliver the full range of HA solutions ranging from simple clustering solutions for application failover in the event of a hardware failure, to high end multiple location cluster solutions. We are providing complete HA solutions on varies platform to meet the different business requirements.
Quantifying Availability
Availability is often expressed numerically as the percentage of time that a service is available for use. For example, a requirement for 99.9 percent availability over a one-year period allows 8.75 hours of downtime; put another way, a requirement for 99.9 percent availability permits only 40 minutes downtime for maintenance every four weeks. Table 1 illustrates the relationship between some common server availability targets and the annual amounts of downtime that they permit.
Table 1 Server Availability and Permitted Downtime
| Availability Target | Permitted Annual Downtime |
|---|---|
| 99% | 87 hours 36 minutes |
| 99.9% | 8 hours 46 minutes |
| 99.99% | 52 minutes 34 seconds |
| 99.999% | 5 minutes 15 seconds |
High Availability (HA) On VMware
Another type of clustering that can be used to increase the availability of a system is quick migration, which can be used with server workloads and applications that normally would not be cluster-aware.
Quick migration combines Windows Server 2008 Hyper-V hypervisor-based virtualization with failover clustering in Windows Server 2008 Enterprise and Windows Server 2008 Datacenter. In quick migration, you run server workloads on virtual machines—guest operating systems running in turn on physical hosts. Each host server is then configured as a node in a failover cluster. If the server initially hosting the virtualized workload fails or requires scheduled maintenance, another server in the cluster hosts the virtualized workload. You can perform any necessary work on the first server and then have it once again resume support services.
Hyper-V Quick Migration for High Availability
Another type of clustering that can be used to increase the availability of a system is quick migration, which can be used with server workloads and applications that normally would not be cluster-aware.
Quick migration combines Windows Server 2008 Hyper-V hypervisor-based virtualization with failover clustering in Windows Server 2008 Enterprise and Windows Server 2008 Datacenter. In quick migration, you run server workloads on virtual machines—guest operating systems running in turn on physical hosts. Each host server is then configured as a node in a failover cluster. If the server initially hosting the virtualized workload fails or requires scheduled maintenance, another server in the cluster hosts the virtualized workload. You can perform any necessary work on the first server and then have it once again resume support services.
High Availability at the Application Level by Microsoft
Reliable hardware keeps individual servers highly available; other high availability strategies keep only the workloads highly available. Microsoft has built features for enhancing high availability into Exchange Server, Microsoft® Office SharePoint® Server, and SQL Server to keep your system up and running.
Microsoft Exchange High Availability
Mailbox databases and the data they contain are one of the most critical components (perhaps the most critical component) of any Exchange organization. In Microsoft Exchange Server 2013, we can protect mailbox databases and the data they contain by configuring your mailbox databases for high availability and site resilience. Exchange 2013 reduces the cost and complexity of deploying a highly available and resilient messaging solution while providing higher levels of end-to-end availability and supporting large mailboxes. Building on the native replication capabilities and high availability architecture in Exchange 2010, Exchange 2013 enables customers of all sizes and in all segments to economically deploy a messaging continuity service in their organization.
SQL Server high-availability
SQL Server high-availability solutions that improve the availability of servers or databases. A high-availability solution masks the effects of a hardware or software failure and maintains the availability of applications so that the perceived downtime for users is minimized.
SQL Server provides several options for creating high availability for a server or database. High-availability options include the following:
- FAILOVER CLUSTERING
- Failover clustering provides high-availability support for an entire instance of SQL Server.
- DATABASE MIRRORING
- Database mirroring is primarily a software solution to increase database availability by supporting almost instantaneous failover.
- LOG SHIPPING
- Like database mirroring, log shipping operates at the database level. You can use log shipping to maintain one or more warm standby databases for a corresponding production database that is referred to as the primary database.
- REPLICATION
- Replication uses a publish-subscribe model. This lets a primary server, referred to as the Publisher, distribute data to one or more secondary servers, or Subscribers. Replication enables real-time availability and scalability across these servers.
- SCALABLE SHARED DATABASES
- The scalable shared database feature lets you scale out a read-only database built exclusively for reporting. The reporting database must reside on a set of dedicated, read-only volumes whose primary purpose is hosting the database.
Oracle Database High Availability
Oracle Database is uniquely positioned in the industry by offering the most comprehensive set of HA capabilities that are available with a single product. Capabilities such as
- Real Application Clusters (RAC),
- Data Guard, Automatic Storage Management (ASM),
- Flashback,
- Recovery Manager (RMAN),
- Online Reorganization, Edition-based Redefinition, etc.
Are available as built-in features of the Oracle Database. Along with complementary products such as Oracle Secure Backup and Oracle Golden Gate, these capabilities work together in an integrated manner to offer the best solution for the Oracle Database to reduce or eliminate both planned and unplanned downtime.
CA ARCserve High Availability
CA ARCserve High Availability software, helps keep your business running with less downtime from unplanned outages and makes continuous data protection easier than ever. It provides high availability for your most critical applications and data, including Microsoft Exchange, SQL Server, SharePoint and Internet Information Services (IIS) and Oracle and BlackBerry servers, as well as your other business-specific applications. CA ARCserve High Availability protects Windows, Linux and UNIX servers, applications and data in both physical and virtualized server environments in your data center and remote offices and can be deployed on-site, off-site and in the cloud. It complements whatever backup solution you use today to provide a more comprehensive strategy for system availability and data protection.
