The downside to an agent-based system is that there is a piece of software that needs to be installed on each server that is going to participate in the archive process. While most operating systems now allow hooks that give the applications a safer mode in which to run, there is always concern about agent stability. Typically, there's also a limited amount of OS support from each supplier of these solutions. Agents that work on NAS solutions like NetApp are almost nonexistent.
The big issue with agent-based data movers is their use of stub files. For some reason, these often prove problematic during operation. Users delete them, they still need to be accounted for (or ignored) by the backup application, and they need to be updated if the archived file is moved a second time.
The positive side to agents is that they are instant. The moment a file reaches a certain age or classification, (an MP3 file, for example), action can happen and data can be moved. They often many times do more than just provide data movement capabilities. Some companies can do indexing of the files as they are archived, others can integrate the archive agent with their backup agent. The other unique component of these solutions tends to be support for tape and optical as an archive target. While disk archiving has its advantages, some customers might want to leverage their existing investment in tape or optical media.
George Crump is founder of Storage Switzerland, an analyst firm focused on the virtualization and storage marketplaces. It provides strategic consulting and analysis to storage users, suppliers, and integrators. An industry veteran of more than 25 years, Crump has held engineering and sales positions at various IT industry manufacturers and integrators. Prior to Storage Switzerland, he was CTO at one of the nation's largest integrators.