Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data recirculation
Patent
1993-03-01
1997-03-18
Psitos, Aristotelis
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data recirculation
360 48, G11B 502
Patent
active
056128290
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a data recording control method of a magnetic tape, and more particularly to a data recording control method applied to a magnetic tape system in which data recording is conducted according to an extended data recording method.
BACKGROUND ART
A magnetic tape subsystem is generally composed of: a magnetic tape apparatus including a magnetic tape, a tape head, and a tape loading mechanism; and a magnetic tape control apparatus. The magnetic tape control apparatus performs a control of a magnetic tape apparatus, which control is required when data are recorded on a magnetic tape (data write), or when data on a magnetic tape are read.
A method called "an extended data recording method" has been proposed as a method of recording data on a magnetic tape. This "extended data recording method" was proposed by ANSI (American National Standard Institution) in 1989 as a method to increase storage capacity per a cartridge tape. The contents of the proposal by ANSI are contained in the following handbook.
"X3B5 EXTENDED MAGNETIC TAPE FORMAT FOR INFORMATION INTERCHANGE 18-TRACK, PARALLEL, 12.65 MM (1/2 in), 1491 CPMM (37 871 cpi) Group-Coded Recording".
A description will now be given of the "extended data recording method" described in this handbook, with reference to FIGS.1 and 2.
In the "extended data recording method", data are recorded on a magnetic tape in accordance with an extended data format as shown in FIG.1. Referring to FIG. 1, a data block recorded on a magnetic tape is composed of a plurality of packets and a count field. The data block has a data block ID and a pad positioned after it. The data block ID is composed of a sector number, an identification code, and a physical block ID. Each packet is composed of a packet header (PH), a data, and a packet trailer (PT), the details of the packet format being shown in FIG.2. Referring to FIG. 2, the packet header PH is composed of a block ID, a packet offset, a packet trailer length, a flag, a reserve, and a CRC (error correcting code), the block ID being composed of an identification code, a sector number, and a logical record ID. The packet trailer PT provided in a non-compressed data packet and the packet trailer PT provided in a compressed data packet have different compositions. The packet trailer PT provided in the non-compressed data packet is composed of a trailer pad and a packet CRC, while the packet trailer PT provided in the compressed data packet is composed of a logical block length, a logical block CRC, a compressed data block CRC, a trailer pad, and a packet CRC. The packet header PH and the packet trailer PT of each packet are the information required when restoring data read from a magnetic tape to an original data, and are formed at the time of data recording so as to be added before and after the data respectively.
In accordance with the above-mentioned extended data format, it is possible to decrease the number of IBG (inter-block gap) which have to be provided between data blocks, because a plurality of packets are combined into one physical block, and data are recorded on a magnetic tape in units of this physical block (data block). As a result of this decrease, the storage capacity per a magnetic tape can be increased.
In order to record data on a magnetic tape in accordance with the above-described "extended data recording method", the magnetic tape control apparatus needs to be equipped with a function called autoblocking. This autoblocking is a kind of data compression technology. In response to a data read/write command given from a host computer for packet units, i.e., for logical block units, the magnetic tape control apparatus processes, by means of this autoblocking function, reads/writes data in the above-mentioned physical block units. For example, when the magnetic tape control apparatus receives a write command WR and data from the host computer, data are recorded on a magnetic tape in the following manner.
Data received from the host computer is compressed, and a p
REFERENCES:
patent: 3916382 (1975-10-01), Martin et al.
patent: 4500965 (1985-02-01), Gray
patent: 5113509 (1992-05-01), Pennings et al.
Hiyamizu Kazufumi
Takai Nobuyuki
Fujitsu Limited
Psitos Aristotelis
Wilson James T.
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