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VTLs can improve recovery but, unlike snapshots or CDP, they're not as simple to deploy. And there's still a physical tape-like recovery process that must be followed because the VTL has to first recover the data from tape if the data has already been moved to tape. However, the ability to capture multiple point-in-time data images throughout the business day, and to directly mount and use a snapshot volume, lets you meet shorter RPOs.
CDP offers benefits similar to those of snapshots, with the added capability of very granular RPOs.
Sometimes a corrupt or deleted file isn't discovered for days, weeks or months. This seems to be a sweet spot for traditional tape backups and virtual tape. While the RPO will be missed because the problem wasn't discovered for some time, noncorrupted data prior to the error is safe and can be recovered.
Storage device failure. Failure of an unprotected drive or a RAID double fault can mean the loss of significant amounts of data. This risk is usually understood and addressed by various types of redundancy.
If additional redundancy isn't implemented or implemented to the appropriate degree, the recovery options are similar to those of detectable file deletion or corruption. Given the amounts of data that can be impacted by this type of error, RPO and RTO are important considerations. Disk-based
| backup technologies may be preferred to meet these objectives.
Interdependency failure. This can be thought of as "effective" data loss due to lack of synchronization or data inconsistency across multiple application components. If one level of service is provided to a portion of an interdependent environment and a different level is provided to another portion, the overall protection is only as good as the lesser of the two levels of service.
While tape can be used for recovery of multiple interdependent data sets, it will likely require cleanup because traditional tape backups have no way to guarantee consistency across apps. Disk-based technologies such as snapshots and CDP often provide some support for consistency groups. It's important to look at the various offerings to determine if they support the type of consistency needed. This depends on whether the disk-based data protection product is host-, appliance- or array-based; depending on where the product sits in the SAN, it will have different knowledge of the consistency of the data between the storage gear it's primarily supporting.
Site failure. The loss of a site falls under the realm of DR. The scale and organizational impact of this scenario differentiates it from more localized operational data-loss scenarios.
Traditional tape backups are still used by many organizations to recover from this type of failure. In all cases, this involves shipping a significant amount of tape from one site to another. Recovery from tape must then be prioritized before the long process of recovering from tape begins. Various VTL products offer a replication capability that can speed this process. However, with VTLs there's still a physical tape-like recovery process if the data has been moved from the VTL to tape.
Disk-based technologies can play a key role in rapid recovery from a site failure. Improvements in network bandwidth and compression technology have allowed many companies to deploy asynchronous or synchronous replication applications to copy live data or snapshots from one location to another.
Some CDP products can also replicate between sites. One of the caveats of traditional replication is that both good and bad data are replicated. By applying a CDP approach to replication, replicated data at the alternate data center could also include the dimension of time so replicas can be rolled back to a granular point in time prior to corruption.
This was first published in September 2008