Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data in specific format
Reexamination Certificate
1997-02-19
2001-05-29
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data in specific format
Reexamination Certificate
active
06239930
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to magnetic data storage media and, in particular, to a method and apparatus for administering a magnetic tape on which can be written video data or computer data.
PROBLEM
It is a problem in the field of data storage systems to manage the storage of video data and computer data that are written on the same type of medium. Magnetic tape has become the industry standard data storage medium for the storage and retrieval of large amounts of data, where the media cost must be kept to a minimum and the data retrieval time is not a critical factor. The data storage capacity has been increased and the media cost of magnetic tape has been reduced by the use of helical scan data recording techniques on magnetic tape for both video data and computer data. Helical scan tape drive systems can make use of either dual reel magnetic tape cassettes or single reel magnetic tape cartridges, both of which use half inch magnetic tape as the recording medium. The dual reel magnetic tape cassette form factor is used in the video recording industry while the single reel magnetic tape cartridge is an industry standard media form factor used in the data processing industry. The selection of the single reel form factor in the data processing industry is desirable due to the fact that automated library systems are presently used to robotically store and retrieve a large number of 3480-type magnetic tape cartridges for an associated plurality of tape drives. Thus, a computer system can access vast quantities of data in a timely manner via the use of the automated library system to retrieve and mount a desired tape cartridgeon a tape drive. In contrast, video cassettes are typically mounted in a video tape drive by a user, with a single tape cassette representing the entirety of the data retrieval process. Thus, the video cassette and computer data cartridge represent data storage media solutions to two diverse and largely mutually exclusive sets of requirements.
In addition, video data differ from computer data in that the video data are presently written in serial form, without the tape drive management of framing information. The video data are presented to the user on a frame basis, yet stored on the magnetic tape on a serial, unindexed basis. In addition, the video data are designed for continuous recording and playback, without error detection and correction being performed on the data. The data are transmitted with any errors that may be included, since by its very nature, video storage and retrieval does not retry a stored data record or play back the data storage medium to correct detected errors. A single pass is all that is available. In contrast, computer data storage systems provide error recovery time in both the reading and writing of data on the data storage medium. It is critical that the data be written correctly and read error free. The data integrity in a computer data storage system is therefore orders of magnitude better than video data storage systems, but computer data storage systems cannot continuously output data as required by video systems due to the error recovery process that is inherent in these systems. Therefore, the video and computer data storage and retrieval systems remain incompatible, in spite of the use of digital recording techniques in the video industry. The medium for both video data and computer data are incompatible, even if they are the same form factor due to the contradictory basic requirements for both systems. Tape drive systems are therefore not equipped to deal with media that can contain either video data or computer data written thereon.
SOLUTION
The above described problems are solved and a technical advance achieved in the field by the method and apparatus of the present invention for administering both computer data and video data that are stored on the same type of data storage medium. This is accomplished by the use of an interface unit that can be located in the control unit of a tape drive subsystem and which determines, when a magnetic tape is mounted in the tape drive, the format that is used to store the data on the magnetic tape medium, such as a 3480-type magnetic tape cartridge he data that are subsequently read from the loaded magnetic tape are then routed to the appropriate data channel in the tape drive subsystem for conventional processing.
In the case of video data, the data are directly written onto the magnetic tape media, while for computer data, a header is interposed between a leader portion of the magnetic tape on the 3480-type magnetic tape cartridge and the remainder of the magnetic tape contained therein. This header segment contains two sections, a first of which is a data record directory that is used by the control unit to denote the location of each data record written onto the magnetic tape as well as administrative information associated with the data record. The second section of the header is an administrative information section that contains data relating to the magnetic tape itself.
In operation, whenever the 3480-type magnetic tape cartridge is mounted in the tape drive subsystem and the magnetic tape contained therein threaded through the tape threading path onto the tape drive takeup reel, the tape drive control unit accesses the header segment of the magnetic tape to read the administrative data written thereon. If a read data record operation is requested and video data are written on the magnetic tape, no header is present and the tape drive subsystem interprets the data recorded on the magnetic tape as video data. In contrast, if a header is present, then computer data are written on the magnetic tape, and the identity of the requested data (data record) is used to scan the data record directory section of the header segment to locate the directory entry relating to the requested data record. Once this directory entry for the requested data record has been located, the control unit can retrieve the information, contained within this directory entry, indicative of the physical position of the requested data record on the magnetic tape. This physical positioning information can then be used by the tape drive subsystem to quickly and precisely position the beging of this data record under the read/write heads of the tape drive subsystem.
Thus, the magnetic tape medium can contain either video data or computer data and the tape drive control unit automatically determines the nature of the data recorded thereon by interpreting the data that are written into the header section of the magnetic tape when the magnetic tape is first mounted in-the tape. drive.
In addition, the tape drive can be used in conjunction with an automated cartridge library system to provide fast access to data of both types, without requiring the automated cartridge library system to maintain two incompatible types of tape drives to service the two types of data. This provides a significant cost savings in that the tape drives are dual function and a single pool of tape drives is maintained in the automated cartridge library for the required data read/write traffic, regardless of the relative quantities of computer data tapes and video data tapes. The single function tape drives would require two pools of tape drives, with the number of drives in each pool having to be set as a function of the relative quantities of computer data tapes and video data tapes.
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Butts Ralph Leon
Dodt William Carl
Donze Jerry Lynn
Egan Brian Patrick
Owens John Craig
Davidson Dan
Duft, Graziano & Forest
Hudspeth David
Storage Technology Corporation
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