Digital data storage system with improved data migration

Digital data storage apparatus having improved backup and providing on-line access to migrated digital files, the apparatus comprising

• primary storage means having a first quantity of storage locations and a first access speed, for storing a first plurality of digital files,
• secondary storage means having a second quantity of storage locations and a second access speed, for storing a second plurality of digital files, wherein the second quantity of storage locations is greater than the first quantity of storage locations and the second access speed is slower than the first access speed,
• backing store means, having a third quantity of storage locations and a third access speed, for storing a third plurality of digital files, wherein the third quantity of storage locations is greater than the second quantity of storage locations and the third access speed is slower than the second access speed, and wherein each of the digital files included in any of the first, second, and third plurality of digital files has an associated characteristic, including file attributes including at least one of, file name, file size, file owner, file protections, time elapsed since a previous access, and type of access,
• secondary storage level detection means for detecting how many of the second plurality of storage locations are being used for storing digital files, and for generating a secondary-storage-full signal when more than a preset number of the second plurality of storage locations are being so used,
• file migration means, in electrical communication with the secondary storage level detection means, with the secondary storage means, and with the backing store means, for automatically migrating digital files from the secondary storage means to the backing store means at selected times, the file migration means including
• file selection means, in electrical communication with the secondary storage means, for selecting, in response to the secondary-storage-full signal, digital files to be migrated from the secondary storage means to the backing store means, and
• stage-out means, responsive to the data selection means, for migrating digital files, selected by the data selection means, from the secondary storage means to the backing store means,
• a baseline-backup means, coupled to said primary storage means, for retrieving from said primary storage means, digital files having a first associated characteristic, for storing copies thereof, and for generating signals representative of storage locations of respective ones of said copies, wherein said copies are referred to as baseline-backup copies, and
• a full-backup, coupled to said primary storage means, for
• i. retrieving, from said primary storage means, digital files for which baseline-backup copies are not stored, or for which baseline-backup copies are stored, but which have been updated since a time of their retrieval from said primary storage means for storage as baseline-backup copies, and for
• ii. storing, along with the full-backup copies, the file identifiers and the storage location-representative signals associated with files for which baseline-backup copies are stored, but which have not been updated since a time of their retrieval from said primary storage means by said baseline-backup means for storing as baseline-backup copies, wherein said storage location-representative signals are indicative of where the baseline-backup copies are stored.