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Agents, Backup Sets, and Subclients Overview
Commvault® software uses agents to provide application-aware data protection using native Application Program Interfaces (APIs) and scripting methods. An example of API-based data protection is using Windows file system APIs to protect files on a Windows server. An example of scripting is using Oracle's Recovery Manager (RMAN) scripts to protect Oracle databases. The agent communicates directly with the file system or application requiring protection. Within an agent, a backup set is used as a primary container, which manages all data the agent is responsible to protect. Within the backup set, one or more sub-containers, called subclients are used to explicitly define data requiring protection and to define specific rules for how the data is protected.
Agent, backup set, and subclient high-level concept 
Agents
Commvault® software provides agents for all major file system and applications. Agent support includes traditional streaming backups, built-in content-aware deduplication, Commvault OnePass® archiving, block-level protection, and hardware snapshot capabilities. It is important to note that these capabilities are inherent in the code and can be enabled within the agent.
Commvault agents are categorized using the following general principles:
- Granular agents including file and mailbox agents
- Database agents
- Hypervisor agents
It is beyond the scope of this document to provide detailed information on all agent support.
File System agents
File system agents provide the fundamental data protection strategy in all data centers. File agents are supported for all major operating systems and include inherent file system capabilities based on the operating system being protected. An example is the ability to use Volume Shadow Services (VSS) to quiesce Windows operating systems.
Application agents
Application agents use application consistent point-in-time protection for application databases. Granular application protection for Exchange, SharePoint, and Lotus Notes provides flexible data protection strategies and simplified recovery methods.
Hypervisor agents
The Virtual Server Agent (VSA) provides complete virtual machine (VM) protection and granular recovery of virtual machine data without the need to install traditional agents within a VM. Based on APIs provided by the hypervisor, different protection and recovery capabilities are possible.
Commvault OnePass® Archiving
Archiving removes infrequently accessed data from production storage. This reduces backup and recovery windows and provides a greater return on investment by reducing production storage footprints. File system data, Network Attached Storage (NAS) data, Exchange mailbox, virtual machines and some database applications support Commvault OnePass® archiving.
IntelliSnap® Snapshot Management
IntelliSnap® technology integrates regular protection methods with hardware-based snapshot technologies to coordinate and manage disk snapshots. This integration allows for application-aware snapshots to be conducted for file systems, applications, and virtual environments.