When used for data backup, storage snapshots enable a physical or virtual machine to be rolled back to an earlier point in time. But because of the way snapshots work, the rollback process can be completed far more quickly than the time it would take to restore a traditional backup.
The term flat backup refers to backups based on the use of snapshots. Although flat data backups were initially very limited in their capabilities, they have evolved to become an option that combines the convenience and simplicity of snapshots with the reliability and flexibility of traditional backups.
The evolution of flat backups
Early on, IT pros were cautioned to treat snapshots as a convenience feature rather than using them as a backup replacement. Because snapshots often reside on the same storage they are designed to protect, a storage failure may result in snapshots being lost. Because of this limitation, flat data backups only became a viable alternative to traditional backups once they provided a way to replicate snapshot data to another location, insulating snapshot copies against various types of failures.
Snapshot replication also opens the door to various disaster recovery options. Some vendors make it possible to attach to a snapshot copy using an iSCSI connection. If a failure were to occur in an organization's primary data center, a remote snapshot copy could conceivably be attached to a physical or virtual machine and brought online within minutes.
Most of the significant improvements that have been made stem from a fundamental change in overall snapshot philosophy. Initially, snapshots were treated as a cohesive unit. If an IT administrator wanted to revert to a previous point in time, they would apply a snapshot to roll back a disk or volume.
Applying a snapshot was typically an all or nothing action. If a snapshot had been created for a volume, legacy flat backup products would enable that volume to be rolled back to a previous point in time. Initially, however, there was no option to use snapshots to recover individual items from that volume. Today, a flat backup can enable the recovery of individual files and applications in a manner similar to that of a traditional backup.
Now that it is possible to work with individual pieces of data inside of a snapshot rather than treating the snapshot as a single entity, backup vendors have been able to implement other functionality, such as snapshot data deduplication.
Another way in which the technology has evolved is by enabling snapshots to be created on demand at various levels throughout the IT infrastructure. Snapshots were originally created exclusively at the disk or volume level, but flat data backups now enable snapshots to be created for virtual machines, and even for entire VMware data stores.
Hypervisors, such as those from VMware and Microsoft, have long included native snapshot capabilities. Today, other vendors have also begun integrating their flat backup products into plug-ins for hypervisor management tools such as VMware's vCenter Server. By doing so, vendors can expose backup-related functionality directly through a virtualization management console. The flat backup vendor then typically provides a much richer set of snapshot-related features than the virtualization vendor can.
Exposing flat backup functionality through a virtualization management console enables administrators to work within a familiar environment and perform snapshot-related tasks on demand, without ever having to leave the virtualization management console.
Flat backup vendors have also begun incorporating snapshot lifecycle management features into their products. For example, some vendors allow retention policies to be set for snapshots, thereby ensuring snapshots remain available for a specific length of time. Similarly, a snapshot can be set to expire after a specific length of time. Expiring snapshots can help to conserve data storage space, and can prevent an outdated snapshot from being applied to a production system.
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