Patent Publication Number: US-7584190-B2

Title: Data files systems with hierarchical ranking for different activity groups

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   The present application is a continuation of U.S. patent application Ser. No. 10/387,120 entitled “Data Files Systems with Hierarchical Ranking for Different Activity Groups” filed Mar. 11, 2003, which claims priority to German application No. 102 11 606.7 filed Mar. 12, 2002, both of which are incorporated herein by reference in their entirety and for all purposes. 

   BACKGROUND OF THE INVENTION 
   The invention relates to a data processing unit comprising a data network, a file server integrated into the data network and having a server data memory and comprising at least one primary data file system, in which data files stored on the server data memory are filed. 
   Data processing units of this type are known from the state of the art. The problem is, however, that, on the one hand, the file servers are intended to ensure quick access to the data files but, on the other hand, an adequate security in the case of failures is intended to be present, and combined with this security in the case of failures the possibility of being able to access the data again as quickly as possible after any failure of a file server. 
   The object underlying the invention is, therefore, to improve the data processing unit of the type described at the outset with respect to its security in the case of failures and the access to the data files following any failure. 
   This object is accomplished in accordance with the invention, in a data processing unit of the type described at the outset, in that the data files of the primary data file system are divided into at least two primary activity groups with a different hierarchical ranking by means of a primary hierarchical memory management in accordance with a primary activity criterion, that the memory management copies at least the data files of the primary activity group with a lowest ranking into at least one secondary data file system on a data memory of a data storage unit positioned subsequent to the server data memory and that the memory management generates metadata from the copied data files of the primary activity group with a lowest ranking. 
   The advantage of the inventive solution is to be seen in the fact that due to the fact that the data files of the primary activity group with a lowest ranking are copied onto a secondary data file system, a data backup already takes place, on the one hand, and, on the other hand, simplified access to these data files is possible following failure of a file server due to the fact that only the metadata must be present on the server data memory in order to be able to access the data files. 
   Metadata within the meaning of this application are data which refer to the location of copies of an original data file and preferably have, in addition, data file attributes or data file descriptions, such as, for example, time stamps, of the original data file. With metadata the memory management has the possibility of finding the corresponding data file in its location. 
   The inventive solution is even more advantageous when data files of a primary activity group with a higher ranking are also copied onto the secondary data file system and when metadata are generated from these data files. 
   In principle, it is possible to keep the data files in the primary data file system in all the cases where the data files of the respective primary activity group are copied onto the secondary data file system and so direct access to the data files can be brought about with the operating system of the file server and, therefore, the data files copied to the secondary data file system represent a backup copy; on the other hand, the metadata do, however, ensure that B if it should be necessary B quick access to the data files copied to the secondary data file system is possible. 
   In principle, it would be conceivable to keep the data files of all the activity groups, from which metadata have been generated, in the primary data file system in order to make them available for quick access by the operating system. 
   This would, however, cause the capacity of the server data memory to increase very considerably. 
   In order to, therefore, keep the capacity of the server data memory within limits, one advantageous solution provides for the data files of the activity group with a lowest ranking, from which metadata have been generated, to be removed from the first data file system. This is possible since copies are present in the secondary data file system and it is possible to locate the data files via the metadata without any problem. As a result, it is possible to keep the capacity of the server data memory within limits. 
   It is, however, also conceivable to remove from the first data file system data files of the activity group with a higher ranking, from which metadata have been generated, in order to reduce the necessary memory capacity of the server data memory even more. 
   With respect to the design of the data memory for the secondary data file system, no further details have so far been given. One advantageous embodiment, for example, provides for the data memory to be formed by a first data storage medium of the post-positioned data storage unit. 
   With respect to the data management of the data files in the secondary data file system, no further details have likewise been given thus far. In principle, it would be possible to store the data files in the secondary data file system simply on the first storage medium. 
   In order to also improve the data integrity of the first storage medium which is intended to be preferably designed such that it allows as quick an access as possible to the data files, it is preferably provided for the data files to be divided in the secondary data file system on the post-positioned data storage unit into at least two secondary activity groups with different hierarchical rankings in accordance with a secondary activity criterion by means of a secondary hierarchical memory management, for metadata to be generated at least from the data files of the secondary activity group with the lowest ranking and the data files themselves to be filed on a second storage medium of the post-positioned data storage unit. 
   In principle, the data files of the secondary activity group can also be kept on the first storage medium in the secondary data file system even though they have been copied and metadata generated from them. 
   In order to create more memory space in the first storage medium, it is, however, particularly advantageous when, in the secondary data file system, at least the data files of the secondary activity group with a lowest ranking are removed from the first storage medium after their filing on the second storage medium and the formation of the metadata. 
   In order to ensure the data integrity as a whole in the secondary data file system, it is preferably provided for the data files of activity groups with a higher ranking to also be filed on the second storage medium in the secondary data file system and metadata generated. This has the advantage that even when the first storage medium fails it is still possible with the metadata to recover the data files from the second storage medium and so the second storage medium represents a backup copy for the first storage medium. 
   With respect to the difference between the first storage medium and the second storage medium of the post-positioned data storage unit, no further details have so far been given. One particularly preferred solution provides for the first storage medium to be a storage medium suitable for quick access to the data and the second storage medium to be a storage medium which is less expensive than the first storage medium and, in particular, to be suitable for the inexpensive mass storage of data files. 
   With respect to the recovery of information concerning the activities of the data files, no further details have so far been given. A particularly preferred solution provides for a filter system which records activities in the primary data file system in a file-related manner to be associated with the operating system of the file server. 
   In this respect, it is particularly favorable when the filter system includes the activities with respect to the data files in the primary data file system in a file-related manner. 
   As a result, it is possible for the filter system to transmit the activities to the primary hierarchical memory management for the formation of the primary activity groups. 
   It has not been excluded within the scope of the preceding embodiments that several secondary data file systems are also present. 
   A particular advantage of the inventive solution is that the metadata are built up such that in the case of several secondary data file systems each data file filed in them can be located in each of the secondary data file systems with the same metadata. 
   For this purpose, it is merely necessary for an additional base reference, which can be set manually or by a configuration in the operating system, to be present for each additional data file system. 
   In conjunction with the preceding description of the inventive solution, the security aspect which results due to the generation of the metadata has been emphasized, wherein this security aspect is present, in particular, when the metadata, for their part, are saved so that in the case of any failure of a server it is possible by using the saved metadata to facilitate quick access to all the data files, from which metadata have been generated, as a result of a small amount of data, namely only the metadata. In this respect, it is merely necessary to copy only the metadata on the storage medium of the file server, with which operations are intended to be restarted, which is quickly possible on account of the small amount of data and, therefore, access to the data files represented by the metadata is made possible again in the shortest possible time. 
   Such a copying or saving of the metadata can take place manually. 
   A particularly favorable solution does, however, provide for a metadata backup management which copies metadata from the server data memory onto an additional data memory. 
   In this respect, the metadata are preferably retained on the server data memory and only additional copies thereof are generated on the additional data memory. 
   With respect to the saving of the data files of the primary activity group, from which no metadata are generated, it is likewise possible to copy these onto an additional data memory by means of a user data backup management. 
   In addition or alternatively to the features of the data storage unit described above, a preferred solution of the object in the case of a data storage unit of the type described at the outset provides for at least some of the data files of the primary data file system to be copied on an additional data memory, for metadata to be generated from these data files and for the metadata to be filed on the server data memory in a metadata file system. 
   The advantage of this inventive solution is to be seen in the fact that the metadata are not filed in the primary data file system but rather in a metadata file system on the server data memory which is separate from the primary system. 
   This solution makes it considerably easier to copy the metadata and, therefore, the entire metadata file system onto additional data memories and, therefore, to provide the security function. 
   In this respect, it is not absolutely necessary with this inventive solution for a primary hierarchical memory management to be present in order to divide the data files of the primary data file system into activity groups. In principle, it would be possible to simply assume with this concept of the inventive solution that metadata are generated from all the data files of the primary data file system. 
   For reasons of a rational operation of the server data memory it is, however, advantageous when the division of the data files of the primary data file system into those, from which metadata are generated, and those, from which no metadata are generated, is brought about via a primary hierarchical memory management, in particular when it is also possible with it to remove some of the data files from the primary data file system and, therefore, not to allow the required memory capacity of the server data memory to become excessive. 
   In principle, it would also be conceivable with this inventive concept to copy the metadata file system manually. It is, however, particularly advantageous when the metadata file system is copied by a metadata backup management onto an additional data memory. 
   Such an additional data memory may be realized in the most varied of ways. One advantageous solution provides for the additional data memory to be a data memory of the post-positioned data storage unit. 
   A different advantageous solution provides for the additional data memory to be the first data storage medium of the post-positioned data storage unit. 
   Another solution provides for the additional data memory to be the server data memory of an additional file server. 
   Such an additional file server can either be a backup file server or a special file server which only serves to take over the operation of the actual file server quickly in the case of any failure of it. 
   Since the inventive concept explained above does not make a primary hierarchical memory management absolutely necessary but this is advantageously used, it is preferably provided, in accordance with this inventive concept, for the at least one section of the data files of the primary data file system to include the primary activity group with a lowest ranking which is generated by the primary hierarchical memory management. 
   An additional, advantageous inventive concept, which accomplishes the object set at the outset and can be used alternatively or in addition to the inventive solutions described above, provides in accordance with the invention, in a data processing unit of the type described at the outset and in the case of data files present on the primary data file system, of which data file copies are present on an additional data memory, for a user data backup management to continuously record alterations to the data files in the primary data file system and for the user data backup management to update the data file copies of the data files, which have undergone alterations, with respect to the alterations with a time delay determined by at least one update criterion. 
   This inventive solution has the advantage in comparison with the known standard backup methods, with which the data are saved, for example, daily or weekly, that a data backup is running continuously, preferably in the background, and it is therefore possible to save the data constantly to an adequate degree in the case of large amounts of data, wherein the advantage is to be seen in the fact that since the backup is constantly running in the background no separate period of time for a data backup is required which is, particularly in the case of large amounts of data, sometimes so great that it is no longer available during customary operating times of a data processing unit. 
   Furthermore, the inventive solution has the advantage that, particularly in the case of alterations carried out several times, each small alteration, which is subsequently corrected again, need not constantly be saved but rather that alterations repeatedly following quickly one after the one lead, in the long run, to the alteration carried out at the end being saved with the time delay. The time delay can, in this respect, be in the time range of minutes, hours or several hours. 
   The simplest possibility would be to determine the time delay as a defined parameter. It is, however, particularly advantageous when the time delay is dependent on several parameters, for example, on the effort required for the respective alteration or also on the relevance of the data file or also the work-load of the file server. 
   Proceeding from a minimum time delay, a particularly favorable solution provides for this to be alterable, in particular, increased in size in a variable manner, for example, in accordance with the predetermined parameters. 
   In order to keep the effort required for the user data backup management as small as possible, it is preferably provided for the user data backup management to record by means of an alteration filter only the data which have undergone alterations and so it is not necessary in the case of the user data backup management B as in the case of the known, customary backup systems B to check through all the data files for alterations but rather to already register the alterations by means of the alteration filter which interacts with the operating system of the file server. As a result, a considerable expenditure of time and operative effort can be saved during the ascertainment of the alterations. 
   Furthermore, it is of advantage, in particular, when the alterations are being carried out, when the user data backup management accesses with a data file update system only the data file copies of the data files which have undergone alterations and carries out the alterations in it so that in this case, as well, it is not necessary to check through all the data file copies. 
   With respect to the filing of the data file copies, no further details have so far been given. It is, for example, particularly advantageous when the data file copies are present in the post-positioned data storage unit. 
   In this respect, it is particularly favorable when the data file copies are present in the secondary data file system of the post-positioned storage unit. 
   In this respect, the data file copies can be present either on the first storage medium or the second storage medium of the post-positioned data storage unit, depending on whether the post-positioned data storage unit operates, in addition, with a secondary hierarchical memory management. 
   It has been assumed for the explanation of the present invention that data file copies already exist for the data files of the first data file system. 
   Data file copies of this type can, in principle, be generated in the most varied of ways. 
   One particularly advantageous solution provides for the data file copies to be made by generating metadata so that in addition to each data file copy metadata also exist which are likewise preferably filed on the server data memory. 
   One particularly favorable solution provides for the data files of the primary data file system to be managed by a primary hierarchical memory management which leaves some of the data files in the first data file system but, nevertheless, generates data file copies and metadata and generates data file copies of a different section of the data files but removes these from the first data file system. 
   As soon as the alteration in a data file, which has been removed from the primary data file system, has, however, taken place, this presupposes that this data file is copied back first of all to the primary data file system again so that following the alteration the data file is, first of all, present on the primary data file system again and the metadata present refer to the data file copy which has not yet been altered. The inventive user data backup management now leads to an update of the data file copies accessible via the metadata, proceeding from the data file present in the primary data file system, likewise with the inventive time delay and, subsequently, to an update of the metadata, as well. 
   In conjunction with the inventive concept of the continuous updating of the user data by the user data backup management, as described above, no details have been given concerning the updating of the metadata. 
   One particularly advantageous inventive concept provides with respect to the metadata for a metadata backup management to continuously detect alterations in the metadata in the primary metadata file system in the case of the metadata, which are present on the primary metadata file system and of which copies are present on an additional data memory, and for the metadata backup management to update the copies of the metadata, which have undergone alterations, with respect to these alterations with a time delay determined by at least one update criterion. 
   The advantage of this inventive concept is to be seen in the fact that the alterations in the metadata in the primary metadata file system are constantly detected and proceeding from the detection of these alterations the copies of the metadata are updated with a predetermined time delay. This has, with respect to the metadata, the same advantages as those which have been explained in conjunction with the user data backup management for the user data. 
   The time delay can also be constant in the case of the metadata. It is, however, even more advantageous when the time delay is variable and dependent on specific marginal conditions for the updating of the metadata, such as, for example, the effort required for the updating of the metadata and the work-load of the filer server or similar parameters. 
   In this case, it is also particularly favorable when a minimum time delay is specified, from which the deviations can then take place due to variable parameters. 
   In order to also reduce the effort required with respect to the recording of the alterations in the metadata, it is preferably provided for the metadata backup management to record by means of an alteration filter only those metadata which have undergone alterations so that no checking through of the entire metadata for alterations is required. 
   Furthermore, the effort required for the updating of the metadata may be reduced in that the metadata backup management accesses with a data file update system only the copied metadata, the metadata of which have undergone alterations, and carries out the alterations in them. 
   In order to have as quick an availability as possible of the data processing system following any malfunction of a file server, one preferred solution provides for access to the data files, for which metadata have been generated, to be brought about in the case of any malfunction of the file server first of all by making the metadata available on the primary data file system of the file server used. 
   The file server used can be the malfunctioning file server when this has been repaired quickly enough and so the metadata used, for example, from an additional data memory are copied back again which can be brought about very quickly in the case of metadata since the metadata form, even for large amounts of data files, a very small amount of data which may be copied onto a server data memory relatively quickly. 
   It is, however, also conceivable for the file server used to be a backup server or a file server provided especially for this purpose which takes over the function of the actual file server in the case of the failure or malfunction thereof and onto which the metadata can then either be copied quickly or are already available as copies. 
   Since the operation of a file server used only with metadata does not allow quick access to the data files but rather this always takes place with delays, it is preferably provided for the continuation of operations, once operation of the file server used has started with metadata, to be brought about by copying data files onto the primary data file system of the server used in accordance with a priority sequence determined from the metadata. 
   Additional features and advantages of the inventive solution are the subject matter of the following detailed description as well as the drawings illustrating several embodiments of an inventive data processing unit. 

   
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  shows a schematic view of a first embodiment of an inventive data processing unit with a file server, the primary data file system of which is organized by a primary hierarchical memory management; 
       FIG. 2  shows a second embodiment of an inventive data processing unit in accordance with the first embodiment but with the difference that several data storage units which are post-positioned are provided; 
       FIG. 3  shows a third embodiment of an inventive data processing unit, with which not only the primary data file system of the file server is organized by a primary hierarchical memory management but a secondary data file system of the data storage unit which is post-positioned is organized by a secondary hierarchical memory management; 
       FIG. 4  shows an illustration of the third embodiment according to  FIG. 3  with illustration of a division of the data files of the secondary data file system to a first storage medium and a second storage medium; 
       FIG. 5  shows a fourth embodiment of an inventive data processing unit which is based on the first embodiment and has, in addition to the file server, a backup file server, as well; 
       FIG. 6  shows a fifth embodiment which is based on the fourth embodiment with respect to its fundamental construction but the backup function is undertaken via the backup server; 
       FIG. 7  shows a sixth embodiment of an inventive data processing unit with a metadata backup management and user data backup management operating constantly; 
       FIG. 8  shows a schematic illustration of functional blocks of the metadata backup management and the user data backup management; 
       FIG. 9  shows a schematic illustration of the time delay provided by the metadata backup management and by the user data backup management for the updating of data file copies; 
       FIG. 10  shows a seventh embodiment of an inventive data processing unit which is based on the principle shown in the sixth embodiment and operates with a metadata backup management and a user data backup management; 
       FIG. 11  shows an eighth embodiment of an inventive data processing unit, with which operation of the backup file server is started with metadata following a malfunctioning of the file server; 
       FIG. 12  shows an illustration of the eighth embodiment according to  FIG. 11  with continuation of operations with additional copying of data files onto the backup server data memory of the backup file server; 
       FIG. 13  shows a schematic illustration of a determination of priorities during the copying of data files onto the backup server data memory and 
       FIG. 14  shows an illustration of a ninth embodiment of an inventive data processing unit, with which a backup server is provided for several file servers. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A first embodiment of an inventive data processing unit, illustrated in  FIG. 1 , comprises a data network which is designated as a whole as  10  and with which a file server  12  is connected. 
   The file server  12  is, for its part, provided with an operating system  14  and a server data memory  16 , in which data files with user data for the data storage unit can be stored. 
   The data files with the user data are thereby stored in a primary data file system  18  on the server data memory  16 . 
   In order to not allow the number of data files in the primary data file system  18  to increase excessively and therefore keep the capacity of the server data memory  16  within a justifiable scope, a primary hierarchical memory management  20  is associated with the primary data file system  18  and this divides the data files of the primary data file system  18  into, for example, three activity groups  22 ,  24  and  26 , namely according to a primary activity criterion which is measured, for example, by how long ago the respective data file was last accessed. Other activity criteria can be data file name, user, access frequency, alone or in combination with one another. 
   For this purpose, a filter system  30  is associated with the operating system  14  and this records accessing of the data files in the primary data file system  18  and passes this to the primary hierarchical memory management  20  so that this divides, for example, the primary data file system  18  into the activity group  22  with a highest ranking, i.e., with access the shortest time ago, the activity group  24  with a lower ranking, i.e., with access a longer time ago and the activity group  26  with a lowest ranking, i.e., with access the longest time ago. 
   Since it is to be assumed in the case of the activity group  26  with the lowest ranking that a current access to these data files on the part of the operating system  14  will take place with only little probability, primary metadata  32  are generated for these data files and filed in a metadata file system  34  on the server data memory  16 . In addition, the data files of the activity group  26  are filed in a secondary data file system  38  on a first storage medium  36  of a data storage unit, which is designated as a whole as  42  and post-positioned, prior to the generation of the metadata  32 . This post-positioned data storage unit  42  is, for example, likewise connected via the data network  10  to the file server  12  and comprises, for its part, its own operating system  44 , wherein a filing of data files in the first storage medium  36  or a second storage medium  46  can be organized with this operating system  44 . 
   The first storage medium  38  is preferably a data memory operating very quickly, for example, a so-called hard disk or a data memory comparable to this with respect to the operating speed and the second storage medium  46  is preferably designed as a storage medium which is less expensive than the first storage medium  36  and, therefore, forms the possibility of an inexpensive mass storage of data files. For example, the second storage medium  46  is formed by a plurality of data carrier cassettes  48  which operate with the most varied of data carriers, such as, for example, tapes or disks, wherein these data carrier cassettes  48  are managed by an archive system  50  and access to the data carrier cassettes is brought about via read-write units  52 . 
   A construction of a post-positioned data storage unit  42  with a first storage medium  36  and a second storage medium  46  is described, for example, in German patent application No. 198 11 034. 
   As a result of the fact that primary metadata  32  have been generated from the data files of the activity group  26  and the data files  26  have been transferred to the secondary data file system  38  of the post-positioned data storage unit  42 , the required memory capacity of the server data memory  16  is reduced since the data files of the activity group  26  can be removed in the primary data file system  18  and are now represented only by the primary metadata  32  stored on the server data memory  16 . 
   The primary metadata  32  are managed under the same data file names as the individual data files of the activity group  26  and comprise, in addition, a reference to the secondary data file system  38 , in which the data files of the activity group  26  are now filed. 
   The metadata for one data file preferably comprise all the relevant data for describing the data file with the exception of the actual user data. The metadata also comprise, in particular, information concerning the time of the last access to the actual data file. 
   If the operating system  14  is now intended to access one of the data files of the activity group  26 , the operating system  14  is stopped and the memory management  20  finds in the metadata  32  corresponding to the respective data file the reference to the data file in the secondary data file system  38  in the post-positioned data storage unit  42 . With this reference, the requested data file is copied by the memory management  20  from the secondary data file system  38  onto the primary data file system  18  again and can then be made available to the operating system  14  for access. 
   As a result of the fact that the data files of the activity group  26  are stored in the post-positioned data storage unit  42  in the form of the secondary data file system  38 , it is also possible, for example,—as illustrated in  FIG. 2  in the case of the second embodiment of an inventive data storage unit B to provide, for reasons of redundancy, an additional secondary data file system  38 ′ or even several secondary data file systems, in which the same data files are filed again for security reasons, wherein the same metadata  32  can be used in order to be able to locate the data files in each of the secondary data file systems  38 . However, in the case of one additional secondary data file system  38 ′ or several secondary data file systems  38 ′ a basic reference is required per additional secondary data file system  38 ′ which can be input either manually or into the configuration of the operating system so that when the secondary data file system used first of all is not available a manual or technical software switchover to an additional secondary data file system  38 ′ takes place. 
   So that the memory capacity of the first storage medium  36  can also be kept within limits, a secondary hierarchical memory management  54  is, as illustrated in  FIG. 3  for a third embodiment, associated with the operating system  44  in the post-positioned data storage unit  42  and this divides the data files in the secondary data file system  38  into activity groups, for example, into secondary activity groups  26   a  and  26   b  in accordance with a secondary activity criterion, wherein the secondary activity group  26   b  has the lowest ranking. 
   The activity criterion used by the secondary hierarchical memory management  54  is also ascertained via a secondary filter system  56  which registers at least one activity criterion of the data files of the activity group  26  and subsequently subdivides the data files of the activity group  26  whether or not this activity criterion is present. 
   As illustrated in  FIG. 4 , on account of the division of the data files  26  into the secondary activity group  26   a  with a highest ranking and the secondary activity group  26   b  with a lowest ranking it is possible to generate secondary metadata  62  for the data files of the secondary activity group  26   b  with a lowest ranking by means of the secondary hierarchical memory management  54  and to store the data files of the secondary activity group  26   b  with a lowest ranking on the second storage medium  46 , for example, on one or more data carrier cassettes  48 , wherein the secondary metadata  62  represent a reference to the filing of the data files from the secondary activity group  26   b  on the second storage medium  46 . 
   In the simplest case, the secondary metadata  62  are still filed in this case in the secondary data file system  38  and also the data files stored on the data carrier cassettes  48  belong logically to the secondary data file system  38 . 
   The generation of the secondary metadata  62  therefore serves merely to keep the capacity of the first storage medium  36  as small as possible since the secondary metadata  62  require less memory capacity than, for example, the data files of the secondary activity group  26   b.    
   It would, however, also be conceivable to file the secondary metadata  62  in a secondary metadata file system  64  on the first storage medium  36 . 
   Furthermore, it is likewise conceivable to generate metadata from secondary activity groups with higher rankings, i.e., for example, also from the secondary activity group  26   a  with the highest ranking and to file the data files themselves on the data carrier cassettes  48  in the second storage medium  46 . 
   In order to make provision for the case where a crash occurs in the server data memory  16  or the server data memory  16  fails for other reasons and, therefore, all the data files themselves are not available, a metadata backup management  70  and a user data backup management  72  which serves the purpose of saving the data files still present on the server data memory  16  are associated with the operating system  14  of the file server  12  in a fourth embodiment of an inventive data processing unit, as illustrated in  FIG. 4 . 
   The metadata backup management  70  operates, for example, with respect to the primary metadata  32  such that it copies the entire metadata file system  34  as such onto the first storage medium  36  and so the copied data files  32   k  of the metadata  32  are present on the first storage medium  36  in a copied metadata file system  34   k.    
   As a result, it is possible at any time, by accessing the copied metadata file system  32   k  of the post-positioned data storage unit  42 , to load this onto a repaired server data memory  16  or a backup server data memory  16 ′ of a backup file server  12 ′ again which can, in principle, be of an identical design to the file server  12  and in the case of a crash of the server data memory  16  can take over the tasks of the file server  12 , as illustrated in  FIG. 5 . 
   In addition, the user data backup management  72  preferably carries out a data backup with respect to the data files of the primary activity groups  22  and  24 , as well, since these could also no longer be used in the case of a crash of the server data memory  16 . 
   The user data backup management  72  therefore copies all the data files of the primary activity groups  22  and  24  of the primary data file system into the secondary data file system  38  so that the data files of the primary activity groups  22  and  24  are present in it as copied data files of the copied activity groups  22   k  and  24   k.    
   As illustrated in  FIG. 5 , it is therefore possible in the case of a crash of the server data memory  16  to also transfer the copied data files  22   k  and  24   k  of the copied activity groups  22   k  and  24   k  to the backup server data memory  16 ′ of the backup file server  12 ′ and, therefore, to have the possibility of using the backup file server  12 ′ as a complete substitute for the file server  12  since not only the data files of the copied activity groups  22   k  and  24   k  are present on its backup server data memory  16 ′ but also the data files of the metadata as copied metadata  32   k  in the metadata file system  34   k.    
   Alternatively thereto, it is, however, also possible, as illustrated in a fifth embodiment of the inventive data processing unit in  FIG. 6 , to file the copied metadata  32   k  in the copied metadata file system  34   k  and the copied data files  22   k  and  24   k  of the activity groups  22  and  24  directly on the backup server data memory  16  when using the backup file server  12 ′ so that any copying and storing of the same in the post-positioned data storage unit  42  is not absolutely necessary or can be carried out only for the purpose of an additional backup. 
   In the case of the functions of the metadata backup management  70  and the user data backup management  72  described in conjunction with  FIGS. 5 and 6 , it is assumed that B as known from the state of the art B a backup copy is made and stored at specific time intervals, i.e., for example, at the end of each day or at the end of each week. 
   The making and storing of backup copies is, however, very time-consuming in the case of large amounts of data. 
   For this reason, in a sixth embodiment of an inventive data processing unit an improved embodiment of a metadata backup management  80  illustrated in  FIGS. 7 to 9  provides for this to determine each time with an alteration filter  84  associated with the operating system  14  whether a data file of the metadata  32  has undergone an alteration or not during access to it. 
   If the data file of the metadata  32  has not undergone any alteration, the alteration filter  84  ignores the access to the data file of the metadata  32  but if the data file of the metadata  32  has undergone an alteration, the alteration filter  84  registers this alteration, designated as V 32 ( t ), of the data file of the metadata  32  as a function of the time t, i.e., as a function of the time, at which the alteration has taken place. 
   The alteration filter  86  of the user data backup management  82  operates in the same way, i.e., if access to one of the data files in the primary data file system  18 , for example, a data file of the primary activity groups  22  or  24  or the activity group  26  does not lead to any alteration in the data file itself, the alteration filter  86  remains inactive. If, however, an alteration in a data file takes place, the alteration filter  86  registers this alteration V 22 ( t ) or V 24 ( t ) of the respective data file as a function of the time t, i.e., as a function of the time, at which this alteration has taken place, wherein in the case of a data file of one of the activity groups  22 ,  24  the data file is present from the beginning on the primary data file system  18  whereas in the case of an alteration in a data file present only in the secondary data file system  38 , this data file is copied onto the primary data file system  18  and is, therefore, likewise present on the primary data file system  18  following the alteration. 
   The alterations in the data files ascertained by the respective alteration filters  84  and  86  are now transferred to a respective data file update system  88  or  90  of the respective metadata backup management  80  or user data backup management  82  ( FIG. 8 ) and this data file update system  88  and  90 , respectively, now causes, as illustrated in  FIG. 9 , an update A  32  or A  22  or A  24  only of the data file in the secondary data file system  38  corresponding to the altered data file but not immediately after the alteration filter  84  and  86 , respectively, has ascertained the alteration V 32 ( t ) or V 22 ( t ), V 24 ( t ) but rather with a time delay which can be specified to the respective data file update system  88  and  90 , respectively, wherein a time delay ZM for the updating of data files of metadata  32  need not correspond to the time delay ZB for the updating of data files of user data from the primary activity groups  22  or  24  but can be entirely different. 
   It is even possible, in the case of the data file update system  90  for the user data, to differentiate between the time delay ZB for data files from the primary activity group  22  and data files from the primary activity group  24  or data files from the activity group  26  and, therefore, to select the time delay ZB differently depending on the primary activity group  22 ,  24 ,  26 , in which the data files are filed. 
   Such an inventive metadata backup management  80  and user data backup management  82  is preferably operated as well during the ongoing operation of the file server  12  so that a continuous updating of the copied data files in the copied metadata  32   k  and the data files in the copied primary activity groups  22   k  or  24   k  is brought about but not immediately following any alteration but rather with a certain delay. This creates the possibility of reducing the effort required in the case of the inventive metadata backup management  80  and user data backup management  82 , particularly when several alterations are carried out in quick succession. In this case, alterations following one another repeatedly at short intervals are not taken into account during the update on account of the time delay ZM and ZB but rather only the alteration in the respective data file, which remains in existence for a period of time which is greater than ZM or ZB, is taken into account. 
   In addition to the reduction in the management effort required, this solution also has the advantage that the user has, with it, the possibility of, where applicable, reconstructing a previous state of the data file from a data file of the copied metadata  32   k  or a data file of the copied primary activity groups  22   k  or  24   k.    
   In the same way as that described in conjunction with  FIGS. 7 to 9 , the inventive metadata backup management  80 ′ and user data backup management  82 ′ can, in a seventh embodiment of an inventive data processing unit, carry out a backup management in the case of data files of copied metadata  32   k  present on the backup server  12 ′ and data files of copied primary activity groups  22   k  and  24   k  so that the backup of the data files on the server data memory  16  is not brought about via the post-positioned data storage unit  42  but rather primarily via the backup server  12 ′ ( FIG. 10 ). 
   In an eighth advantageous embodiment of an inventive data processing unit, illustrated in  FIG. 11 , the activity criterion of the primary hierarchical memory management  20  is selected such that the data files in the activity group  22  with the highest ranking remain in it only for the shortest possible time, for example, fractions of seconds or minutes and are then incorporated into one of the activity groups  24  or  26  with a lower ranking. 
   The data files of both activity groups  24  and  26  are transferred to the secondary data file system  38  and the metadata  32 ′ are then generated from the data files of the two activity groups  24  and  26  and filed in the metadata file system  34 ′. 
   However, the data files of the activity group  24  are not removed from the primary data file system  18  but rather remain present on the primary data file system  18  since these are current data files, to which constant access on the part of the operating system  14  takes place. Only the data files of the activity group  26  are removed from the primary data file system  18 , as already described in conjunction with  FIGS. 1 and 2 . 
   Furthermore, the metadata  32 ′ are filed on the backup file server  12 ′ as copy  32 ′ k  as metadata file system  34 ′ k.    
   As an additional security measure, it is, however, also possible to file a second copy of the metadata  32 ′ as  32 ′ k  and of the metadata file system  34 ′ k  on the first storage medium  36  of the post-positioned data storage unit designated as  42 . 
   In this embodiment, the metadata backup management  80 ′ operates in the manner which has already been described. 
   On the other hand, the user data backup management  82 ′ operates such that in the case of any alteration in a data file from the activity group  24  in the primary data file system  18  an update of the data file of the activity group  24  in the secondary data file system  38 , which can be located by means of a data file of the metadata  32 ′, is likewise brought about with a predeterminable time delay ZB. If the updating of the data file of the activity group  24  in the secondary data file system  38  has been brought about, an adjustment of the corresponding data file of the metadata  32 ′ then takes place and, subsequently, an adjustment of the corresponding data file in the copied metadata  32 ′ k  by the metadata backup management  80 ′ not only on the backup server data memory  16 ′ but also on the storage medium  36  of the post-positioned data storage unit  42 . 
   If a data file of the activity group  26  is altered, the corresponding data file is again filed in the server data memory  16  via the metadata  32 ′ and, as a result, the update of the copied data file in the activity group  26  in the secondary data file system  38  takes place automatically in comparison with a data file of the activity group  22  or  24  and following alteration thereof B as already described in conjunction with a data file of the activity group  24  B with the corresponding time delay ZB and, following updating of the corresponding copied data file, the updating of the copied metadata  32 ′ k  by the metadata backup management  80 ′. 
   If, in this embodiment, a crash occurs in the server data memory  16 , it is accepted that data files of the activity group  22  will be lost. Since all the new data files have, however, been allocated to the activity group  24  or the activity group  26  after a very short time, this loss is slight and can be accepted without any problem. 
   As a result of the fact that the backup server  12 ′ is, however, in possession of the copied metadata  32 ′ k  for the data files of the primary activity groups  24  and  26 , the backup server  12 ′ can, apart from the data files of the activity group  22 , make available all the remaining data files of the primary activity groups  24  and  26  to the operating system  14 ′ but with a certain delay in time since the corresponding data file must first of all be retrieved from the secondary data file system  38  via the metadata  32 ′ k  on the backup server  12 ′. 
   This system does, however, have the advantage that restarting of the data storage unit is possible very quickly since it is possible to make available again to the operating system  14 ′ via the backup server  12  in the shortest possible time the data files from the activity groups  24  and  26  requested by it. 
   Furthermore, it is possible B as illustrated in  FIG. 12  B following a restart of the system by means of the backup file server  12 ′ to retrieve the data files of the activity group  24  into the primary data file system  18 ′ again. 
   For this purpose, a reactivation system  100  runs in the background on the backup file server  12 ′ and this checks through all the metadata  32 ′ k  in the copied metadata file system  34 ′ k  and on the basis of the data file description data present in the metadata and one or more predeterminable priority criteria PK determines the sequence, in which the data files are intended to be retrieved from the secondary data file system  38  into the primary data file system  18 ′ of the backup server  12 ′. 
   As illustrated, for example, in  FIG. 13 , the reactivation system  100  checks through the metadata  32 ′ k first of all to see whether these fulfill the highest priority criterion PK 1 . All the data files in the secondary data file system  38 , which belong to the metadata which fulfill the priority criterion PK 1 , are then copied onto the primary data file system  18 ′ of the backup file server  12 ′. 
   Subsequently, the metadata  32 ′ k  are then checked to see whether they fulfill the priority criterion  2 , i.e., a lower priority criterion. All the corresponding data files are then copied from the secondary data file system  38  onto the primary data file system  18 ′ of the backup file server  12 ′ again so that after a short time at least the data files of the activity group  24  which have the most current priority, if not all the data files of the activity group  24 , are again present in the primary data file system  18 ′ of the backup file server  12  and, therefore, the backup file server  12 ′ is in a position to operate almost exactly as quickly, if not as quickly as the file server  12 . 
   In this respect, it is to be emphasized that the retrieval of the data files from the activity group  24  by the reactivation system  100  takes place in the background and so parallel thereto the operating system  14 ′ can still access, via the metadata  32 ′ k , the data files from the activity groups  24  and  26  requested directly by the operating system  14 ′. 
   A ninth, advantageous embodiment of the inventive data storage unit, illustrated in  FIG. 14 , operates with several file servers  12   1 ,  12   2  and  12   3  which all communicate with one another via the data network  10 . 
   Each of the file servers  12   1 ,  12   2  and  12   3  operates in the way described in conjunction with the embodiment according to  FIGS. 11 to 13 , i.e., the primary hierarchical memory management  20  has data files in the activity group  22  of the primary data file system  18  present for only a very short time and classifies the data files in the shortest possible time either in the primary activity group  24  or  26 , as has been described in conjunction with the embodiment according to  FIGS. 11 to 13 . 
   In this embodiment, the metadata  32   1,2,3  of the metadata file system  34   1,2,3  are copied by means of the metadata backup management  80 ′ in each of the file servers  12   1 ,  12   2  and  12   3  onto the backup server data memory  16 ′ so that this has the metadata file systems  34   k   1 ,  34   k   2 ,  34   k   3  with the metadata  32   k   1 , to  32   k   3 . 
   The backup file server  12 ′ is therefore in a position to permit access to the data files of the activity groups  24   1,2,3  and  26   1,2,3  in the shortest possible time in the case of any failure of one of the file servers  12   1  to  12   3  since the metadata  32  required for this purpose are available immediately on the backup file server  12 ′ and can be used to copy the required data file from the secondary data file system  38  on the backup server data memory  16 ′ for its operating system  14 ′. 
   The same components are used in all the embodiments insofar as the same reference numerals are utilized and so reference is made to the first respective description of the corresponding components.