The IBM 3850 Mass Storage System[1] (MSS) was an online tape library used to hold large amounts of infrequently accessed data.[2] It was one of the earliest examples of nearline storage.[3]
Starting in the late-1960s IBM's lab in Boulder, Colorado began development of a low-cost mass storage system based on magnetic tape cartridges. The tapes would be accessed automatically by a robot (known as an accessor) and fed into a reader/writer unit that could work on several tapes at the same time. Originally the system was going to be used as a directly attached memory device, but as the speed of computers grew in relation to the storage, the product was re-purposed as an automated system that would offload little-used data from hard disk systems. Known internally as Comanche while under development, IBM management found a number of niche uses for the concept, and announced it officially as the IBM 3850 on October 9, 1974. After more than a decade (comparable to the IBM 2321 Data Cell, 1964–1975), it was withdrawn August 5, 1986.
The Mass Storage System consisted of a library of cylindrical plastic cartridges, two inches wide and 4 inches (100 mm) long, each holding a spool of tape 770 inches (20 m) long storing 50 MB; each virtual disk required a pair of cartridges. These cartridges were held in a hexagonal array of bins in the IBM 3851 Mass Storage Facility. New cartridges were rolled into the facility and were automatically stored in a vacant bin. The data were accessed via virtual IBM 3330 disk drives, and physically cached on a combination of 3330 and 3350[a] staging drives, the data being transferred automatically between cartridge and disk drive in processes called staging and destaging. These were all connected together with the IBM 3830 Storage Control (also used for disk storage alone), the entire system making up a 3850 unit.
Cartridges were moved into and out of read stations by two motorized accessor arms, electrically connected via flat cable on a drum. Stage time for data from cartridge to disk was typically 15 seconds, including about two seconds to move the cartridge into a read station, and eight to ten seconds to read the 200-foot tape.
El método de grabación era inusual para su época. La unidad sacó la cinta del cartucho y la enrolló una vez alrededor de un mandril cilíndrico en forma de hélice , luego detuvo la cinta. El cabezal de la unidad , montado en un tambor giratorio, luego se gira una vez para leer o grabar una pista diagonal. Luego conduzca, luego enrolle la cinta un pequeño paso hacia adelante y el cabezal gire para hacer la siguiente pista. Dependiendo de las definiciones técnicas, esto podría incluso considerarse un primer ejemplo de grabación de escaneo helicoidal digital , mucho antes de la unidad helicoidal de Exabyte (que se basaba en sistemas de grabación helicoidal de vídeo analógico desarrollados anteriormente).
Cuando se requirió espacio libre en el disco, se seleccionó un grupo de cilindros para pasarlos a cinta, estos se transfirieron con un cambio de formato mínimo o nulo. Cada cinta podría almacenar 202 imágenes de cilindros de 19 pistas cada una, la mitad de los 404 cilindros en un paquete de 3330 discos. Las ubicaciones de los cilindros en la cinta se fijaron e identificaron mediante marcadores a lo largo del borde.
Había varios modelos del 3851 disponibles. El A1 más pequeño tenía 706 cartuchos que almacenaban 35,3 GB, mientras que el A4 más grande tenía 4720 cartuchos que almacenaban 236 GB en una unidad de 20 pies (6,1 m) de largo. Todas las unidades también estaban disponibles en los "modelos B", que agregaban un segundo controlador para copias de seguridad en línea, así como almacenamiento fuera de línea. Se lanzó una segunda serie el 6 de marzo de 1980, duplicando la capacidad máxima a 472 GB. Toda la serie se suspendió el 5 de agosto de 1986.
{{cite book}}: |work=ignorado ( ayuda )