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One of the great benefits of continuous data protection is that the technology makes it easy to establish multiple layers of protection. But to truly protect data, an organization must have at least three copies of it:
- The original working set of data
- A local backup of the data
- A remote backup of the data
A CDP system provides the tools necessary to create redundant data copies.
The mechanisms for data redundancy vary from one vendor product to the next, but many continuous data protection (CDP) system products include a built-in replication engine that replicates data from the primary backup server to a secondary backup server as well as to tape.
A popular architecture is disk-to-disk-to-tape (D2D2T) backup, which replicates data from the primary backup server to a secondary backup server. The data from the secondary backup server is then periodically copied to tape for off-site storage. In a CDP system that supports disk-to-disk-to-disk replication, the secondary backup server replicates data to yet another backup server rather than to tape.
Also gaining popularity in recent years is disk-to-disk-to-cloud architecture, which involves two CDP servers and a cloud storage gateway. The servers adhere to a D2D2T architecture, while the cloud storage gateway emulates a virtual tape library. The secondary backup server thinks it is replicating data to tape, but data is actually sent to a cloud storage gateway and then, ultimately, to public cloud storage.
Although many CDP products have built-in replication engines, there are other ways to replicate data that has been backed up. Because a CDP system writes data to a disk-based storage array, it is sometimes possible to perform storage array-level replication, thereby achieving redundancy without incurring the cost of an additional backup server.
CDP has been discussed primarily from the standpoint of protecting file data, but offerings exist to protect other types of data, such as databases or virtual servers. Some newer CDP products offer an instant recovery feature for virtual machines in which a VM may be run directly from the backup while a restoration completes in the background.
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