Methods and apparatus for backing-up and restoring files using multiple trails

Mechanisms and techniques are disclosed that provide the ability to backup and restore a file between a backup server and a data storage system using multiple trails of data for the same file. Within the data storage system, the file is generally stored as a series of data portions spread across multiple storage devices such as disk. The file may be stored, for example, within a volume. In the backup operation of the invention, a discover phase determines which respective data portions of the file (e.g., partitions) are stored upon which respective storage devices (e.g., disks) of a plurality of storage devices. The system then designates individual respective backup devices (e.g., tapes) of a plurality of backup devices to be used for backing-up respective individual ones of the data portions of the file that are stored on respective storage devices. Next, the system concurrently backs up at least two respective data portions of the file to different respective backup devices for which those data portions are designated, such that at least two respective data portions of the file are backed-up to respective backup devices in parallel. The restore operation operates in a similar manner by determining which respective data portions (e.g., backup images) of the file are stored upon which respective backup devices (e.g., tapes) of a plurality of backup devices. The system then designates individual respective portions of storage devices of a plurality of storage devices to be used for storing respective individual ones of the data portions of the file that are stored on respective backup devices. Next, the system concurrently restores at least two respective data portions of the file to different respective storage devices for which those data portions are designated, such that at least two respective data portions of the file are restored to respective storage devices from respective backup devices in parallel. By treating portions of a file as separate backup work items, each portion may be provided as an independent stream or trail of data to or from the backup server, thus decreasing the time required to backup or restore a file.