Editor's note: This SearchStorage.com contributor Randy Thorburn takes a different approach to finding the right technology to use in a storage solution. Instead of arguing whether you should use disk or tape technology, he argues that moving to a more automated approach that uses intelligent agents to make that decision is the best way to figure out whether your data will be backed up on tape or on disk.
The debate over the virtues of using tape versus disk technology as a backup medium is centered around the argument that disk accepts data faster but has space, cost, and long-term viability issues. On the other hand, tape is a better long-term storage medium but has access performance issues. This leads most people to the conclusion that you should use both technologies which appears to be a viable solution, except when you consider the fact that existing backup software is extremely limited in its ability to seamlessly take advantage of hard disk and tape in a single storage environment.
Some backup software products write to hard disk using a virtualized tape format. This makes it easy to move protected data to tape after it's on disk. However, you don't get the random access advantages of disk so you end up losing most of the performance benefits. Other products can write to hard disk in a native filesystem format, but they use a simple TAR or copy command to migrate backed-up data to tape for long-term safekeeping. While this works, you compromise security. It also requires a two-step process to retrieve the data back from tape to the disk cache, then to the restore location. Some products suggest doing the same backup twice. The first backup session runs to hard disk and a second session, covering the same data, sends it to tape. The overhead associated with this is obvious.
Data protection doesn't have to be so constrained. Configurations for data protection should be designed around the performance and longevity requirements of the data that's being backed up, rather than the limitations of the software managing the environment. Ideally, under this school of thought, we would abandon the debate of disk vs. tape and simply have a data protection system that works for the user, instead of the other way around.
Let the agents do the action
For decades, technology has existed that allows software solutions to manage data protection configurations in a manner flexible enough to meet the needs of any environment. The Distributed Computing Environment (DCE) was originally designed as part of Apollo Domain OS in the 1980s. One component of DCE is a location broker agent, which enables the connection between clients and servers, in a client/server environment, to be dynamic. DCE has evolved to be a common element in almost every operating system available today. Use of the location brokerage service is common in printer sharing and other software, where several resources may change their status and state frequently.
An ideal data protection configuration will have several storage resources available, some of them based on access performance and some based on storage longevity. A solution utilizing the location broker agent of DCE lets backup clients choose the storage resource best suited for their data, based on rules applied to the backup set configuration. Critical data encountered by the backup system is sent to a storage resource with high access performance while non-critical data can be sent to a storage resource with lower access performance.
Another concept is to equip the servers with backup client capabilities. Backup clients locate data eligible to be backed-up based on rules and schedules, and send it to storage for safekeeping. Applying these same principles to a storage server enables it to migrate and/or replicate protected data to other storage devices in the environment. For example, a client backing up critical data will locate and send its data to a hard disk storage resource to get it protected as quickly as possible. A client-like agent on the storage server then locates all data that arrives on its storage device and moves or copies it to whatever tape-based storage resource is available, therefore backing up the data on two storage devices. To enhance the system, you could add data retention policies that leave backup data on the disk-based storage resource for three days and on the tape-based storage resource for a month.
Along with changes in our information-centric world, it'd be ideal to see some new, refreshing approaches to data protection. After all, with the technology available today, we should have the ability to design storage protection programs to meet the needs of any environment, no matter how flexible the situation requires.
For more information on backups:
Off-site copies on the cheap
About the Author: Randy Thorburn is vice president of marketing for Avail Solutions, a San Diego-based provider of data protection software.