Double-Take
For Windows Servers

Ready access to mission-critical data and applications is absolutely necessary in today’s rapidly expanding, technology-driven business environment. The Double-Take Software file replication and failover product offers an effective solution to reduce downtime and keep businesses operational.

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Power outages, hardware malfunction, software failure, human error, and natural disasters are the most common causes for system downtime. The cost of downtime can range from lost business and productivity to cessation of operations, depending on the severity and duration of the failure. Double-Take Software helps minimize the risk to business through real-time local and remote replication of critical data. Double-Take also provides timely server and application failover.

The core of Double-Take Software technology is its patented real-time file delta replication. After performing an initial mirror of selected drives, directories, and/or files, Double-Take subsequently replicates—in real-time— only the byte-level changes to those datasets, instead of copying whole files across the network every time they change. For example, once a mirror of a large database file has completed, Double-Take then replicates only the changes within the file as they occur. This significantly reduces the amount of time and bandwidth necessary to transmit the data.

Double-Take uses standard TCP/IP to transmit data over a local area network (LAN) or a wide area network (WAN) with bandwidth throttling and encryption as options. Its support of multiple operating systems (including Microsoft Windows NT/Windows 2000/2003 and cross-platform replication that can be controlled from a common management console) help gear Double-Take toward today’s heterogeneous server and storage environments. Simple Network Management Protocol (SNMP) integration and a complete command line interface allow automated monitoring and administration of Double-Take via enterprise management systems.

The feature-rich functionality of Double-Take and its flexible configuration options can help provide many different types of protection suited for a variety of business requirements.

Local High Availability

Double-Take can be configured to provide local server and application fault tolerance. Critical data is identified on a source server and mirrored to a target server. Replication of subsequent changes can take place on either a real-time or scheduled basis. Both mirroring and replication can be sent over a public or dedicated network link.

One-to-One Monitoring and Failover of a Source Server

In a one-to-one scenario, an active or passive target server is set to monitor the health of a source server, assuming the identity and functions of the source server if a failure occurs(see Figure 1).

Users can configure both the failover time and the failover process itself, which can be set to “automatic” or“manual.” During failover, the IP address, computer name, and data share points of the source server are transferred to the target server. Pre-failover and post-failover scripts can be run on the target server to quickly start up applications and/or services in order to resume normal operations with little or no delay to end users.

Many-to-One Monitoring and Failover of Multiple Source Servers

In a many-to-one scenario, the same procedure can be repeated to allow a single target server to monitor and stand in for multiple source servers (see Figure 2). Double-Take provides failover support for file and print services in addition to support for major applications such as Microsoft Exchange Server, Microsoft SQL Server, Microsoft Internet Information Server(IIS), Oracle®, Lotus Notes®, and SAP.

Off-Site Disaster Recovery

Double-Take offers additional protection from geographic or site disasters through remote replication of mission-critical data for off-site disaster recovery (see Figure 3). The use of TCP/IP makes Double-Take easily deployable over a WAN. Its highly efficient byte-level replication dramatically reduces network load, effectively allowing replication of critical data over slower remote links that would otherwise be impractical, if not impossible, to use.

For remote replication, bandwidth throttling allows bandwidth utilization to be limited to designated levels to balance the replication with other remote network traffic. The ability to schedule remote replication can also help accommodate other remote network traffic as well as reduce transmission costs in cases where tariffs favor periodic bursting of multiple packets over intermittent streaming.

The Double-Take asynchronous data replication technology also minimizes performance impact on the source server that could otherwise be associated with slower remote links or an occasional loss of remote connectivity.

Geographic Cluster Protection

Companies with investments in clustering technology understand the need for ready access to mission-critical data and applications. Yet, some may overlook their continued vulnerability to geographic or hardware-related disasters until it is too late. The reliance of clusters on a single shared storage unit limits their ability to protect against such disasters.

Double-Take adds another layer of protection to clustered environments by replicating cluster data to other local destinations and/or safely off-site (see Figure 4). Additionally, Double-Take’s failover engine enables local failover from one cluster to another cluster or stand-alone server, providing protection against cluster failure and allowing routine cluster maintenance. Double-Take works equally well in Active/Passive and Active/Active cluster configurations and is also compatible with both Microsoft Cluster Service and NetWare Cluster Services.

Double-Take Software recently introduced the GeoCluster™ add-on, which allows the geographic separation of two nodes in the same Microsoft cluster through replication of cluster data and management of the quorum resource, thereby eliminating the shared storage requirement.

Storage Consolidation and Enhanced Backup

The distributed nature of many storage environments presents a great challenge to administrators in their efforts to provide enterprise data protection. While local server backups prevent undue load on the network, they are difficult to manage in a distributed environment. Centralized tape backup of multiple servers is more manageable, yet increases network load and may prevent backups from completing when faced with a shrinking backup window.

Double-Take’s many-to-one data replication handles these challenges, especially consolidating storage for the purpose of centralized tape backup. Using its patented byte- level replication, Double-Take can efficiently send changes from multiple production servers to a dedicated backupserver—oftentimes connected to a storage area network(SAN) to accommodate large amounts of data—with minimal impact on the production servers or the LAN (seeFigure 5). Because backups are performed on the target server and storage devices, they can be run as frequently as necessary without affecting production.

Double-Take also eliminates open file issues and the need for open file agents. Regardless of file state on the source servers, changes to selected files are captured as they occur and are immediately sent to the target server. If a file on the target is temporarily being backed up as changes occur on a source server, the changes are queued and then automatically applied to the target server once the file is released. Double-Take is fully compatible with third-party backup software products from VERITAS®, Computer Associates, Legato®, BEI, and others.

Other Applications, Support, and Services

Double-Take’s one-to-one and cross-platform replication make it ideal for server and operating system (OS) migration. Failover further eases the server migration and OS upgrade process, allowing a seamless cut over to the new server when ready. Customers also use the Double-Take one-to-many replication for automatic content distribution from one to multiple load-balanced servers in a front-end Web farm.

Double-Take is a multifaceted tool that minimizes downtime and helps companies stay open for business. Crucial to the equation is the availability of 24×7 technical support and implementation services. With its robust features and flexible configuration options, Double-Take achieves enterprise-class data protection for businesses that cannot afford to have anything less.

Additional Resources

For additional information on Double-Take Software or GeoCluster:

Call : 020 8657 5762 in United Kingdom & Ireland (Lyonesse Software)
Call : 727-562-0101 in North America (Sunbelt Software)
Call : +33 (0)1 47 77 05 00 rest of Europe (Sunbelt, France)

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