DE4325710C2 - Method for controlling a drive device for tape-shaped digital data carriers connected to a program-controlled device - Google Patents

Description

The invention relates to a method according to the preamble of claim 1.

With the development of tape recorders for digital sound recording drawing and reproduction in the field of entertainment electronics became devices - known as DAT recorders (digital audio tape) - created in principle as a memory can be used for digital data. In front especially for small to medium-sized data processing facilities complexity and for special program-controlled ones directions such as B. communication systems, make DAT run works because of their small size and uncomplicated graceful handling when changing the cassette form ideal storage facilities for information representations that require a large storage volume, right relatively rarely needed, should be changeable and at Power failure must not be deleted. Moreover, are with DAT drives fast access times when reading and Writing data achievable.

Magnetic tapes are used as data carriers for DAT drives uses that in its physico-chemical structure similar to conventional analog tapes. A magnetic tape for a DAT drive is or is being formatted, i. H. on the Ma gnetband are individually selectable areas - data blocks  or called blocks - defined in which information are storable. The magnetic tape is sort of as one Understand chain of data blocks, their respective beginning is electromagnetically marked on the magnetic tape and from Drive is recognizable.

The information to be stored on the magnetic tape is Amounts of data called files and each a variety of related information units exhibit. As a rule, several data blocks are required, to save a file.

Saving information on the tape, too Write process or write access is subject to one essential characteristic - the sequential access; d. H. every write operation on the tape erases, at least lo gisch, all following a respective writing point formations on the tape.

So far, only the individual were on one tape Files saved. When reading the tape or when closing When accessing a file, a file catalog was created that enable faster access to the individual files should. The file catalog had to be like every time it was started which are newly created.

The object of the present invention is to provide a method admit with which the time expenditure and thus the system loading a program-controlled device to scream or reading files can be kept to a minimum.  

This object is achieved according to the invention by the Drawing part of claim 1 specified features.

A major advantage of the invention is that the file catalog is saved behind the files on the tape because the file catalog can be changed without it that relevant information on the tape z. B. Zer files be disturbed. In addition, the copying time in the event of a change of the file catalog can be minimized.

Advantageous developments of the invention are in the Un claims specified.

A major advantage of further training is that that it is easy to see whether the file catalog on the tape is valid or complete.

Based on the drawing, an example is given below game explained in more detail. Show:

Fig. 1 is a schematically highly simplified Blockdarstel lung for the essential components of a per program-controlled device and for a device connected to this DAT drive,

FIG. 2a, b is an illustration of orientation to illustrate the format and the availability of a tape with data blocks and files

Fig. 3 is a flowchart illustrating individual process steps in reserving and releasing a tape.

In Fig. 1, the essential components of a program-controlled device DVA are roughly simplified, to which a DAT drive is connected as a mass storage device. The program-controlled device can, for. B. be a communication system that serves to connect communication terminals and communication networks. From the special edition of "telcom report""ISDN in the office", Siemens AG, 1985 z. B. known under the name "HICOM" a communication system. The DAT drive DAT can be arranged as an integrated unit in the program-controlled device DVA or as an independent, for. B. portable device.

The program-controlled device DVA usually has at least one processor device UP, a read-write Memory area RAM, a program memory area ROM, as well as a "hard disc" HD drive. The above Components are interconnected via a bus system the bus system also being connected to an interface module TC via which the DAT drive DAT is connected is. The DAT drive is a standard, commercial one device available on the market. The used Recording format is standardized and used by many Manufacturers used.

In conjunction with a programmable device in Form of a communication system, the drive DAT z. B. used for programs and data when switching on, ie when Read the system startup into its working memory, and outsourced software components available if required to have or to save software and data. So that can the security and archiving of data in particular  of communication subscriber-specific data guaranteed will.

The DAT drive is controlled via standardized commands that transmitted to the DAT drive via a SCSI connection bus will. The control is done by the Processor device UP, the associated control program from the random access memory RAM or program memory ROM takes.

One available as a disk for the DAT drive Magnetic tape BD is in a cassette and provides a length of z. B. 90 m a storage capacity of 2 GB to disposal.

Although files stored on the tape BD in any Order can be read is a letter only sequentially possible. Assuming none To be able to use temporary storage means that a new file just after the last valid one on the tape file can be attached or that only the last valid file can be replaced. If only one Bytes in an existing file all subsequent bytes of this file and all subsequent ones Files on the tape deleted.

Attention is also drawn to DAT drives on a Provide at least two "partitions" for the tape, whereby Write operations in one "partition" have no influence take the data in the other "partition". In the following but is only from a "partition" on the tape went out.  

In FIG. 2 is illustrated by way of example, what kinds of information are stored on a tape BD. On the tape BD data blocks BL of the same size are set up, which act as frames for storing a large number of information units, e.g. B. of 512 bytes. The beginning of each block is marked electromagnetically, the marking having a block number by means of which the drive DAT can specifically search for a block BL and position it on a read / write head. Starting from the beginning of the tape, the blocks are assigned ascending block numbers.

Identification data ID is at the beginning of the tape BD deposited, e.g. B. the name of the tape, an identification number, the Date of first use etc. The Identification data can be one or more Blocks, but are rarely more than need one or two blocks.

Following the identification data ID, beginning with the beginning of the next free block - block 2 in the example - files D1, D2, D3 are stored. Each of the files starts at the beginning of a block. The file D1 stored in the first place begins with the second block and ends in the fifth block. Each file consists of a header HE and a user data part ND adjoining this header HE. The header data part HE is e.g. B. 512 bytes long and contains file-specific information, for. B. the file name, file attributes, user identification data, the length of the file, the checksum etc.

Following the total of the files D1, D2, D3 stored on the tape BD, a so-called file catalog DK is stored, which begins at the beginning of the next free block - block 11 in the example. The file catalog DK is made up of a general part AT and this subsequently arranged individual file parts DIT.

The general part AT contains information that is refer to the tape as a whole, e.g. B. the version number, the name of the data set, the block size, the number of deleted files, the "logically deleted" bytes, the Number of files on the tape as well as the number of total bytes used. For everyone on the tape BD saved file is a file-specific part of DIT in which u. a. the file name in question, the File position, i.e. the block number in which the header HE the file is stored, the file length in bytes etc. are deposited.

Following the file catalog KD, a "meta file catalog" MDK is also stored on the tape BD, which usually occupies only one block - block 13 in the example shown. This meta-file catalog MDK stores information that, by its very nature, can be understood as organizational control information. Among other things, the time of first use, the tape name, the block size, the number of files listed in the file catalog, the number of bytes in all files, the logically deleted files in the file catalog, the number of bytes of the logically deleted files etc. are stored. At the beginning of the next free block following the metafile catalog MDK - block 14 in the example - there is an end of data marker EOD which makes the end of the information valid on the tape recognizable for the drive.

FIG. 3 shows a sequence of control steps which are initiated by the program-controlled device DVA when the tape is reserved, ie after the tape has been inserted into the drive and when the tape is released, ie before the tape can be removed. Even with a "restart" of the program-controlled device DVA, z. B. after a system failure, these control steps are performed.

First of all, the DAT drive receives an instruction to search for the data end marking EOD, ie the drive is to position the data end marking EOD on the read / write head. Then the drive DAT is given the instruction to position a block in the direction of the beginning of the tape, that is to say the beginning of the block - in the figure block 13 - to the read / write head of the drive DAT. Then the drive receives a control instruction to read the data of the set block, whereby the metafile catalog MDK is read, which is transferred into the read-write memory area RAM of the program-controlled device DVA.

The DAT drive also receives a command, the Search for the beginning of the band, the first block, and the one there read stored identification data ID, which also in the RAM program-controlled device DVA are transmitted.  

The reading of those stored at the beginning of the tape Identification data ID is used for a comparison with im Meta file catalog MDK stored identification data. At the comparison can determine whether in the case one for a failure of the program-controlled device DVA following "restart" the one on tape BD File catalog DK is valid, i.e. completely from the hardware Disc HD was written back, or whether when writing the File catalog DK an error has occurred, e.g. B. at one System failure.

So if the identification data, e.g. B. the band name or similar in the MDK metafile catalog are the same as the am Identification data ID stored at the beginning of the tape, so can can be assumed that the file catalog DK and the Meta file catalog MDK are complete and consistent. If Differences when comparing the identification data this is a sign that the File catalog DK may be prior to system failure has not been updated or just was copied incompletely. In such a case after restarting the system the file catalog can be rewritten on the tape or the file catalog DK must be from the information on the tape File headers HE can be created again.

Of course, the positioning of the tape BD on the beginning of the tape and reading the identification data ID also before positioning on the data end marking EOD respectively.  

Is a when comparing the identification data Agreement has been found, the im Meta file catalog MDK read information the first Block of file catalog KD determined. This is the number of files with the length of an individual file Multiply catalog part DIT and to whole blocks rounded up, from which knowledge of the block number of the the block containing the metafile catalog MDK Block of the file catalog DK can be determined.

The drive receives instruction on the determined first Position the block of the file catalog DK and the Read the entire catalog of files. Of the File catalog is in the hard disk HD of the program-controlled Device DVA copied. If a file D1 is to be read, So it is first saved in the HD on the hard disk File catalog DK searched for the relevant file and its Initial block determined. Then the drive becomes Positioning of the start block concerned and read the file D1.

If a file is to be written on the tape, it will Drive to the next, the last saved file D3 positioned on the belt following the free block and the File written. In the DK file catalog on the HD hard disk a corresponding file-specific part DIT added.

If the tape is to be released, the Intended to remove the tape from the drive, the File catalog DK copied from hard disk HD to tape BD starting with the first free block after the  last block occupied by the last file. In connection to the file catalog DK is the meta file catalog MDK in the next free block written. The meta file catalog MDK following block then assigns the data end marking EOD on.

Because the file catalog DK at the end of the saved files, it can be restored without subsequent files being destroyed. Accordingly, only the file-specific part DIT of the File catalog DK are written back to the file-specific part DIT for a file to be deleted or file to be renamed follows because the meta file catalog MDK after the file catalog DK is saved. The position at Which of the file catalog must be written can be from the information in the file-specific part DIT for the last file or from the MDK in the meta file catalog determine stored information.

Claims (3)

1. A method for controlling a drive device (DAT) connected to a program-controlled device, in particular a communication system, for a tape-shaped digital data carrier which is used to store files consisting of a header information (HE) and a subsequent user data information (ND). D1, D2, D3) is used and the data blocks (BL), which are arranged one after the other and can be selectively positioned on a read / write head, are used to store a large number of digital information units, with information units stored below becoming invalid when the data carrier (BD) is accessed, characterized in that that, in a reservation of the data carrier (BD) and after start-up of the program controlled device (DVA) to a, a Datenendemarkie tion (EOD) having data end block is positioned such that a data end block disposed above Since tenblock positioned in the a meta file catalog (MDK) is stored, which is read at least partially, that is then positioned on a first block of a file catalog (DK) stored in front of the meta file catalog (MDK) and that the file catalog (DK) is for transfer to program-controlled device (DVA) is read. 2. The method according to claim 1, characterized in that at the beginning of the tape of the data carrier gers (BD) is positioned and identification information tion (ID) is read, which is used for a comparison with an in identification in the metafile catalog (MDK) formation is provided.   3. The method according to claim 1 or 2, characterized in that prior to releasing the data carrier (BD) to the one saved by a last one File (D3) occupied data blocks following the first free Data block is positioned starting with that block the data transmitted by the program-controlled device Teikatalog (DK) is written and that afterwards on the positioned next free block and the metafile catalog (MDK) is written.