Today's workforce requires immediate access to information, applications, coworkers and customers. Both large and small enterprises are increasingly online, mobile and Web 2.0-driven. These advancements illustrate that IT is no longer just a business tool; it is business.
Yet every year businesses experience the effects of data loss stemming from information technology (IT) network outages - whatever the origin - and as IT systems fail, daily operations follow, and the results can be fatal.
In tough economic times, as well as in prosperity, businesses should strive to create a high availability infrastructure that responds robustly to new-age business challenges and disruptions. Data replication solutions can play an important role in implementing high availability. They can also serve as a cornerstone to effective business continuity (BC) and disaster recovery (DR) strategy and - good news - they can be very affordable.
Host-based Data Replication
Smaller businesses often choose host-based solutions because they are the most cost-effective and least-complicated systems to install. This type of implementation, often referred to as server clustering, occurs at an organization's operating level by pairing two or more separate servers that each save the same data, ensuring redundancy.
Server clustering provides three key benefits:
- High Availability: It is designed to avoid a single point of failure
- Scalability: Computing power can be increased by adding more processors or computers
- Manageability: The servers appear as a single-system image with a single point of control
In a clustering scenario, the back-up server can be deployed remotely, potentially eliminating any need to restart the server should an interruption occur. Additionally, clustering offers efficiency and a limited footprint, both in terms of floor space and energy consumption. Clustering for high availability allows automated failover between servers in the cluster, providing close monitoring of applications and all their components, including operating system, server hardware, networking and storage.
While clustering provides significant benefits, IT managers should also understand its related challenges. A clustered environment can seem very foreign, especially if the technology is new to the staff. If IT is unable to perform basic checks, such as confirming whether a patch was applied correctly to all nodes in a cluster, the system is vulnerable to serious outages. Also, if the SMB is using Service-Oriented Architecture (SOA), where applications are working in tandem, it will require solutions that factor in the dependencies.
Finally, keep in mind that host-based solutions employ a variety of software systems, all of which likely will require a license. The clustering software determines when to perform a failover by continually checking each application's "heartbeat" signal, and if one system has a problem, the application on another server in the cluster takes over. To the outside world, the cluster appears as a single system, but intelligent redundancy within it creates high availability.
Controller-based Data Replication
The second form of data replication, controller-based, is typically found in larger organizations and replicates data at the byte-level onto a storage area network (SAN) - an architecture that connects remote storage devices to servers - while appearing attached locally to the operating system. Often more expensive than host-based solutions, controller-based data replication is an enterprise-class solution that can be implemented in two ways - each with advantages and disadvantages.
- Synchronous Replication: Synchronous replication, commonly referred to as disk mirroring, is the recording of redundant data on two partitions of the same disk or two separate disks, for fault-tolerant operation. Mirroring is a central component in the highest level of data protection and disaster recovery, and it differs from ordinary backups which simply replicate a complete volume at specific points in time, often for use in testing. Mirroring creates dynamic, real time copies of data volumes, which further reduces the amount of data at risk of loss. Mirroring can be done using Level 1 Redundant Array of Independent Disks (RAID) features. RAID can be provided through the motherboard or a controller card, or built into a dedicated disk array
The benefits of data mirroring include:
- Protection Against Data Loss: Added redundancy offers backup in case of hardware failure
- Disaster Protection: Offers quick recovery against site- and region-wide incidents
- Individual Disk Access: Each disk or set of disks in the mirror can be accessed separately for reading purposes
Although mirroring is essential to ensuring high availability of data, it is not a complete data protection solution by itself. Mirroring is ineffective if the data is corrupted. For example, a virus might corrupt or erase data, or a user might accidentally delete data. This is why data protection in the form of regular backups is also necessary for file-level protection
- Asynchronous Replication: The alternative controller-based method is asynchronous replication. The biggest difference between synchronous and asynchronous replication is that data stored on an asynchronous system is not replicated immediately. It is stored first at its primary site and then replicated to the second site at user-prescribed intervals. This data latency is critical and bears a higher level of business risk because, should an event occur, any unreplicated data will be lost
Advice for IT
When determining which data replication solution best fits your organization, the first objective should be to decide the recovery point objective (RPO) and recovery time objective (RTO). The RPO is the amount of data loss the organization is willing to sustain, while the RTO is the amount of time it is willing to live without its business critical applications - the maximum tolerable outage.
Implementing clustering and mirroring as part of a healthy high availability solution and BC/DR plan should be managed seamlessly to maximize the benefits. Consider the following additional best practices:
If your organization has not yet committed to either a host-based or controller-based solution, keep in mind that it is very difficult to switch between the two because they are incompatible. Each method is unique and uses different components (hardware to software and vice-versa). If you are unsure about which type is right for your businesses, be sure to seek the guidance of a trusted advisor.
About the Author
Mike Lapetino is a storage specialist with CDW, a leading provider of technology products and services for business, government and education. Lapetino works directly with account managers and customers to identify and procure storage solutions that meet their unique needs."