# Archive Indexing

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The Archive index is a special database that stores mapping information for video archive. This database includes which cameras are archived, for which times, and in which chunks exactly the archive is stored. (Chunks are the building blocks of video storage, see "To find archive on a storage device".)

The client application pulls storage chunks to the Timeline based on the information in the archive index database. When you click on the Timeline to play a given recorded segment, the client sends the server a request for that video. The server checks the archive index to determine where video for that particular moment is stored – on which drive and in which exact chunks. The server reads that particular video and sends it to the client to display.

| - Client - Server - Archive Index database - Storage disk

There can be situations when information in the archive index doesn’t reflect the actual video archive. For example, if a disk has failed or been removed, the information about recordings which are supposed to be on that disk will still be in the archive index, but the server will not be able to read the disk.

Similarly, sometimes there is no information in the archive index about archive that does exist in storage. This can happen if a camera has been deleted from the System. Video recorded from that camera is kept, but information about it is deleted from the archive index.

These problem can be fixed by archive reindexing. During that process, the server will scan all recordings on all drives and update the archive index database with the current information. Archive reindexing is initiated from the Storage Management dialog for each server, and can be performed for main or backup storage locations. See "Reindexing Archives".