IBM 3850
The IBM 3850 Mass Storage Subsystem was a mass storage subsystem from IBM . It was a forerunner of today's tape libraries and made it possible to manage data on virtual disk storage .
Structure and functionality
The IBM 3850 Mass Storage Subsystem consisted of a kind of high-bay warehouse , the IBM 3851 Mass Storage Facility , in which cylindrical magnetic tape cassettes (so-called cartridges) were stored in hexagonal honeycombs. These cartridges were 2 inches (5.08 cm) in diameter and 4 inches (10.16 cm) high. The length of the magnetic tape was 770 inches (19.55 m). Using oblique recording technology, 50 MB could be saved on each cassette. Two cartridges each formed a virtual hard disk of the type IBM 3330-1 .
The honeycombs were arranged along the two walls of the IBM 3851. A robot transported the cassettes from the honeycomb to the writing and reading stations. An input / output station was used to introduce new and eject old, defective cassettes.
The built-in control unit managed an inventory of the cartridges, the MSS Volume Inventory , which was stored redundantly on two disks, the table packs . The table packs were not directly accessible from the operating system of the connected mainframe. The microprogram of the control unit, which was coded as an overlay program and whose parts were loaded into the core memory as required, was also stored on the table packs .
The MSS also included a number of disks, the so-called staging drives . These were initially of the type IBM 3330 (1 or 11), later also of the type IBM 3350 , which was operated in 3330 compatibility mode. The staging drives were managed by an IBM 3830 Storage Control (Model 3).
The IBM 3850 had an integrated error correction process . As soon as the number of correctable errors in a cassette exceeded a threshold value, the contents were copied to an empty cassette, the inventory was updated and the old cassette was ejected.
Models
The IBM 3850 were available in different models, some of which could also be converted. Basically there were A and B models, the latter containing an additional control unit. The smallest model, the A1, was able to store a total of 35.3 GB on 706 cartridges, the A4 had 236 GB.
IBM 3850 and MVS
So-called virtual units had to be defined in the MVS operating system . As soon as an application requested files from the MSS, the data was written from the corresponding virtual hard disks in blocks of 4 cylinders to the staging drives and could be read from there like normal disk files. This process was called staging . After the close, the data was written back to the cartridges (so-called destaging ), but remained on the staging drives for as long as possible.
The MSS was administered using special IDCAMS commands. There were also paid additional programs such as MSVIZAP.
history
In the late 1960s , the IBM laboratory in Boulder, Colorado began developing a mass storage subsystem under the code name Comanche . On October 9, 1974, it was officially announced as the IBM 3850. The IBM 3850 experienced a real boom in the early 1980s . Since IBM was behind schedule with the delivery of the IBM 3380 disks , a number of companies were forced to procure an MSS with technology that was already out of date in order to cope with the data growth. Support for the IBM 3850 ended on August 6, 1986.