Cloud disaster recovery or traditional DR?

A disaster is anything that causes unplanned downtime to a server or application that impedes an organisation’s functioning. This means a disaster can be caused by an isolated hardware failure, data corruption on a storage system, or even an administrator accidentally shutting down a server. Disaster Recovery (DR) is the ability to restart applications, reconnect users and other applications,and restore data.

When speaking of DR, the recovery point objective (RPO) and recovery time objective (RTO) are the two key metrics. RPOs measure how much data the organisation can afford to lose, and RTOs are a measure of how quickly the organisation can get back up and running.

Traditional DR involved replicating data and applications on dedicated backup servers and storage either on-premise or at remote locations, and employing qualified IT personnel to create regular backups, test, and maintain this duplicate IT infrastructure. This was an expensive and unaffordable overhead for many companies. Worse, the whole process of restoring data from backup devices such as tapes, CD, or DVD and initializing and running applications on backup servers meant that data transfer was error prone and recovery times were slow – recovery times of several hours or few days were the norm.

Cloud DR offers a compelling alternative to traditional DR. Instead of buying and maintaining backup storage and server resources that are brought into use only in the event of a disaster, cloud computing - with its pay-per-use pricing model - allows businesses to pay for long-term data storage and only pay for servers during testing or failover. This significantly reduces cost and makes DR affordable for most enterprises.

Cloud DR provides virtual machine snapshots of physical or virtual servers at the primary data centre. The organisation pays for storing the snapshots, application data in a suspended state, and replication of data from primary to the secondary (cloud DR) site for data synchronisation. It pays for the infrastructure-as-a-service feature only in case of a disaster when snapshots of primary servers need to be brought online as a substitute for the primary site.

Low RTO (Lower downtime): With cloud disaster recovery services, the DR site can be brought online within seconds or minutes—as opposed to a physical DR site which could take minutes (if not hours). In addition, data loss is directly related to downtime. A cloud DR site that boots up within a few seconds translates to data loss of just that timeframe. Moreover, a cloud-based disaster recovery service can still be set in motion from a laptop using a wireless internet connection, or better yet, in an automated fashion before the administrator even notices an outage has occurred.

Feasible for small to midsize organisations: Even small and medium-size companies can afford it, as it’s considerably less expensive than building or leasing fully-mirrored secondary data centres. Cloud-based DR enables organisations to immediately failover VMs, reconnect users via VPN or Remote Desktop Protocol, and orchestrate failback to rebuilt servers in the customer data centre.

Virtualized cloud platforms are well suited to providing DR. Under normal operating conditions, a cloud based DR service may only need a small share of resources to synchronize from the primary site to the cloud. The full resources required to run the application only needs to be provisioned (and paid for) in the event of an actual disaster.

The inherent on-demand nature of cloud computing provides the greatest cost-benefit when peak resource demands are much higher than average demand. This means that cloud platforms can provide the greatest benefit to DR services that require warm stand-by replicas. The cloud can be used to maintain the state of an application using low cost resources under ordinary operating conditions, and the more powerful and expensive full resources to run the full application need to be invoked only when disaster strikes. These additional resources can be provisioned in seconds or minutes. In contrast, in traditional DR, backup servers must be always available to address a full disaster workload – this results in significant idle capacity and cost during normal operation.

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