In computer storage, a tape library, sometimes called a tape silo, tape robot or tape jukebox, is a storage device which contains one or more tape drives, a number of slots to hold tape cartridges, a barcode reader to identify tape cartridges and an automated method for loading tapes (a robot). One of the earliest examples was the IBM 3850 Mass Storage System (MSS), announced in 1974.
These devices can store immense amounts of data, currently ranging from 20 terabytes[1] up to more than 366 petabytes of data,[2] or about seven hundred thousand times the capacity of a typical hard drive and well in excess of capacities achievable with network attached storage. Typical entry-level solutions cost around $10,000 USD,[3] while high-end solutions can start at as much as $200,000 USD[4] and cost well in excess of $1 million for a fully expanded and configured library. For large data-storage, they are a cost-effective solution, with cost per gigabyte as low as 10 cents USD, or at least 60% less than most hard drives, and they also provide systematic access to very large quantities of data. The tradeoff for their larger capacity is their slower access time, which usually involves mechanical manipulation of tapes. Access to data in a library takes from several seconds to several minutes.
Because of their slow sequential access and huge capacity, tape libraries are primarily used for backups and as the final stage of digital archiving. A typical application of the latter would be an organization's extensive transaction record for legal or auditing purposes. Another example is hierarchical storage management (HSM), in which tape library is used to hold rarely used files from file systems.
Contents |
There are several large-scale library-management packages available commercially. Open-Source support includes AMANDA, Bacula, and the minimal mtx program.
Tape libraries commonly have the capability of optically scanning barcode labels which are attached to each tape, allowing them to automatically maintain an inventory of which tapes are where within the library. Preprinted barcode labels are commercially available or custom labels may be generated using commercial or free software. The barcode label is frequently part of the tape label, information recorded at the beginning of the media to uniquely identify the tape.
Smaller tape libraries with only one drive are known as autoloaders.[5] The term autoloader is also sometimes used synonymously with stacker,[6] a device in which the media is loaded necessarily in a sequential manner.[7]
Other types of autoloaders may operate with optical disks, floppy disks and compact discs.