When thinking about business continuity, you want to be able to keep systems available and at the same time be able to recover from data loss if and when it happens. Being able to provide availability to business-critical systems as well as recover from data loss involves two different core concepts and sets of underlying technologies. These are “high availability” (HA) and “disaster recovery” (DR).
There can be confusion on the role that both play in allowing organizations to maintain business continuity. Additionally, due to budgets or other factors, businesses may choose to implement one or the other. However, both are needed to maintain true business-continuity. What constitutes high availability and disaster recovery? What are the differences between the two? Why are both high availability and disaster recovery important in maintaining business-continuity for organizations?
What is High Availability (HA)?
High Availability is the combination of mechanisms in place that allow for uptime of services, applications, and data. This concept and the underlying HA technologies are what allow organizations to maintain SLAs of uptime such as the “four nines”, etc. High Availability mechanisms and technologies are in place for routine outages that may be the result of hardware failure, network failure, load-induced outage, or another application failure. High availability events may include the following:
- Hardware failure – This may be of a component within a single server, network switch, cabling, or another physical dependency that causes an outage
- “Split brain” scenarios – If a server or node in a cluster becomes isolated, the cluster can still maintain “quorum” by isolating the failed node and ensuring the service or application is still available
Examples of High Availability technologies include:
- VMware has VMware “High Availability” built into the VMware ESXi cluster utilizing vCenter server. If a host fails, the VM will be restarted on a healthy host.
- VMware has VMware “High Availability” built into the VMware ESXi cluster utilizing vCenter server. If a host fails, the VM will be restarted on a healthy host
- Hyper-V high availability clusters also leverage the underlying Windows Cluster technology to provide similar high availability to virtual machines.
- Windows Clustering provides high availability for applications and services such as Microsoft SQL Server, File Servers, and other services
- Network load balancers provide redundancy and load balancing capabilities that allow spreading loading across various nodes as well as providing redundancy
- Engineering other basic high availability may involve having multiple network switches so there are redundant paths for data to travel. Having multiple power supplies and UPSs provide high availability from a power standpoint. Generators can provide high availability when utility power is disrupted
VMware vSphere HA and Proactive HA
While planning for high availability is a crucial component of a business continuity plan, HA does not protect organizations against more ominous major disasters. This is where Disaster Recovery or DR comes into play. What is disaster recovery? What technologies are involved with providing disaster recovery mechanisms?
What is Disaster Recovery (DR)?
While high availability protects you from the more routine interruptions to service, disaster recovery protects you from major disasters where data may be lost. While the focus of high availability is uptime on a daily basis, disaster recovery comes into play when extreme outages are experienced. Disaster recovery takes into account all the scenarios that high availability is not meant to handle. What are some examples of disaster recovery events?
- Natural Disasters – Natural disasters as a result of earthquakes, fires, floods, tornadoes, and hurricanes are extraordinary events that surpass the business-continuity that high availability provides
- User induced data loss – An administrator or a normal end user may delete business-critical data
- Security breaches resulting in data loss – If an attacker gains access to key business systems, data can be intentionally lost or corrupted
- Catastrophic site failure where all resources in a geographic location are unreachable
Examples of Disaster Recovery technologies include:
- Backups
- Offsite DR Copies
- Replication
Backup of business-critical systems is at the core of disaster recovery. Backups allow restoring files, databases, or even entire physical or virtual machines where data may be lost or otherwise corrupted or unusable
Offsite copies of backup data is part of the 3-2-1 backup methodology as it provides resiliency in the backup itself. Having a copy offsite ensures having copies of backup data if the primary copy is lost
Replication creates a replica copy of a virtual machine in a DR site. With each backup iteration, these changes are replicated to the standby VM. The virtual machine that exists in the DR site is for all practical purposes an exact copy of the production virtual machine at the time of the replication interval
Vembu BDR Suite provides Backup, Replication, Offsite DR, and Recovery
Why Do You Need Both High Availability (HA) and Disaster Recovery (DR)?
It is important to use both high availability AND disaster recovery technologies to ensure business continuity. As described, high availability protects you from the day to day events that may interrupt system availability such as a hardware failure, network failure, load-induced outage, or another application failure. Having high availability mechanisms and technology in place to ensure that these types of failures result in only minimal or no impact, results in having a highly available system. Disaster recovery comes into play when a major outage is experienced as a result of natural disasters, user induced data loss, security breaches or site-wide failures.
By obtaining backups of business-critical systems and keeping offsite DR copies, you have resilient backups that are available to restore data in a disaster event resulting in data loss. Replication ensures you are protected in a site-wide disaster where an entire site may be offline. By replicating virtual machines to a DR facility, resources can be rerouted to the DR site in the event the main production site goes down. Both high availability and disaster recovery are extremely important in business-continuity planning. Each plays a critical role in ensuring both day-to-day uptime as well as data recoverability in the event of a major disaster.
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