Backup and Data Recovery Converge
Over the last few years the functionality provided by backup and disaster recovery systems have converged so that they now appear to be the same – at least on the surface.
Historically, backups have been based on making data copies while disaster recovery comes into play after a disaster happens. Backups and other fault-tolerant mechanisms are put to work to bring things back to operational condition.
While, historically, backups were stored on removable media, they have now given way to a continuous process wherein data is copied to disk based storage arrays — a mode of backup called continuous data protection (CDP).
Today’s data protection systems solve many problems of the past
Continuous data protection systems can backup data a single time rather than repeatedly. A single copy retains changes as they’re updated. In these systems, data can be rolled back to a point before which hardware failure or data corruption occurred.
Using a strategy in which single recovery data is available, it’s a good idea to make certain that the backup storage array and the backup server don’t become a single point of failure. To prevent this, data replication to an alternative storage device is prudent. Replication could also be to cloud storage or a tape library.
Continuous data protection has become a popular data backup strategy, as it deals with problems of data growth and increasingly limited backup windows. Continuous data protection is not scheduled by definition.
Snapshot, virtualization and replication play a major role in convergence
These three technologies are key players in the convergence of backup and disaster recovery technology. The reason is simply that recovering from a disaster can be accomplished without traditional data restoration. Instant recovery can occur while storage cost is minimized.
A differencing disk is a virtual hard disk, VHD, which is reserved to record changes in case they need to be backed out. A snapshot process redirects write operations to a differencing disk. These two concepts are essential to understanding instant recovery.
Instant recovery makes full-blown restoration unnecessary whenever there’s a copy of the data available online. The failed system can utilize data available on the backup storage array.
How do differencing disks and snapshots come into play? A snapshot is created before a failed server is allowed to use the data residing on the backup array. The snapshot results in the creation of a differencing disk. The failed server can use the data from the backup array for read operations. Writing takes place on the differencing disk.