Abstract:
A method and apparatus for protecting file data is provided that combines or merges revision based backup with backup based on time intervals. One embodiment is directed to a method for protecting data contained in a file of a computer system, wherein the computer system is useable to create multiple successive file versions. The method comprises the steps of specifying a maximum number of file versions that can be stored collectively at first and second storage locations, and apportioning the maximum number into a first number of file versions and a second number of file versions. The method further comprises storing the most recent of the multiple file versions, up to a number equal to the first number, at the first storage location. A number of file versions respectively created before the stored most recent versions, up to a number equal to the second number, are stored at the second storage location, over a pre-specified time period and in accordance with a pre-specified strategy.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention disclosed and claimed herein generally pertains to an improved method and apparatus for providing continuous data protection for files in computers and data processing systems. More particularly, the invention pertains to a method of the above type that uses a combination of both revision based and time based techniques to provide continuous protection for computer file data. Even more particularly, the invention pertains to a method of the above type wherein users are enabled to easily select different file protection strategies, in order to accommodate widely varying protection requirements for different types of files. 
         [0003]    2. Description of the Related Art 
         [0004]    Businesses are increasingly concerned with protecting their computer data. Losing key business information can hamper productivity, cause application outages, and result in project delays and diversion of resources. Many businesses are also legally required to formally deploy data protection. In addition, data residing in work stations and laptops is frequently unprotected, even though such data can amount to 60-70% of data used by businesses such as law firms, medical practices and consulting firms. In these types of enterprises, loss of data can be particularly significant in impacting productivity and viability. 
         [0005]    At present, a common approach for protecting data in computers and data processing systems is to back up data on a scheduled basis, at pre-specified time intervals. For example, at the end of a specified period, such as the end of each work day or work week, backup copies are made of particular data files, and the copies are placed into cache storage. Data protection systems made by companies such as Iomega Corporation and Microsoft Corporation operate according to this type of pre-scheduling. However, it often happens that the most valuable files are those that a user is currently working on. For files of this type, it can frequently become necessary to access a backup file copy that is more recent than the last backup copy that was made on a prescheduled basis. For example, numerous changes could have been made to a file since the last scheduled backup. 
         [0006]    To meet this need, continuous data protection techniques have been developed. In a continuous data protection system, backup copies are generated in response to data revisions, rather than at prescheduled times. In systems of this type, whenever changes made to a file are saved, thereby creating a new file version, a backup copy of the new version is immediately created, and then moved to cache storage. One example of systems of this type is the Tivoli® Continuous Data Protection (CDP) of International Business Machines Corporation (IBM). In revision based CDP systems, all of the most recent versions of a file are continuously stored in a cache memory, up to a pre-specified maximum number. When the maximum number is reached, the oldest stored version is removed from the cache, to make room for the newest version. 
         [0007]    Notwithstanding the benefits of re-vision based CDP systems as described above, such systems generally do not allow file protection procedures to be adapted by a user, in order to meet different needs for different types of files. Systems that back up files on fixed time schedules, as likewise described above, do not provide such flexibility. However, requirements for retaining prior file versions can vary widely for different types of files. For example, keeping previous versions of financial data files can be very important, whereas previous versions of emails may be of little or no importance. Some files may be revised frequently, while others are seldom or never revised. Moreover, it is generally not desirable to use storage capacity to retain file versions that are redundant, or that do not need to be saved for other reasons. In revision-based CDP, some users save often, in an effort to be careful with their data, but ultimately destroy their revision history. Accordingly, a more flexible solution is necessary to meet more advanced requirements that are common today. It would be very advantageous to provide a file protection system that could be selectively adapted or adjusted, in order to meet different backup requirements for different types of files. 
       SUMMARY OF THE INVENTION 
       [0008]    Embodiments of the invention generally pertain to a method and apparatus for file data protection that combines or merges revision based backup with backup that is based on a period of time. One embodiment of the invention is directed to a method for protecting data contained in a file of a computer system, wherein the computer system is useable to create multiple successive file versions. The method comprises the steps of specifying a maximum number of file versions that can be stored collectively at first and second storage locations, and apportioning the maximum number into a first number of file versions and a second number of file versions. The method further comprises storing the most recent of the multiple file versions, up to a number equal to the first number, at the first storage location. A number of file versions respectively created before the stored most recent versions, up to a number equal to the second number, are stored at the second storage location, over a pre-specified time period and in accordance with a pre-specified strategy. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
           [0010]      FIG. 1  is a schematic diagram showing respective components for an embodiment of the invention. 
           [0011]      FIG. 2  is a timeline that further illustrates an embodiment of the invention. 
           [0012]      FIG. 3  is a flowchart showing steps for implementing an embodiment of the invention. 
           [0013]      FIG. 4  is a block diagram showing a data processing system that may be used in implementing in an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]    Referring to  FIG. 1 , there is shown a computer or data processing system  102  that may be of virtually any type. Computer  102  is exemplified in  FIG. 1  as a laptop computer by way of illustration, but is by no means limited thereto. Computer  102  is capable of generating files of many different kinds that each contain data, wherein all such files can be revised or changed over time. It is therefore necessary to provide means for protecting the current versions of these files. In addition, it is necessary to protect earlier versions of some or many of the files, in case the earlier versions must be referred to at some time in the future. As described above, different types of files can have very different protection requirements. Accordingly, it would be beneficial to differentiate between different file types in providing file protection, so that versions of some files would be retained, without expending resources to save file versions of other files that were not important. It could also be beneficial to adapt file retention practices to the comparative frequency with which changes are made to different file types. 
         [0015]    To accommodate these respective needs, a server  106  is provided with a file storage manager  108 , wherein manager  108  operates in accordance with an embodiment of the invention. More specifically, manager  108  is interconnected to computer  102 , and directs the protective storage of file versions for different files. For a particular file  104 , a total or maximum number of current and prior versions that can be saved is specified, such as by a default condition or by user selection. As described hereinafter in further detail, a portion of this maximum number is assigned or allocated to a revision based file protection mode. Thereafter, versions of the file resulting from successive saved changes, up to the allocated number, are continuously stored in a local recent version cache  120 , such as in disc  112  of computer  102 . 
         [0016]    After the allocated number of versions has been stored in the recent version cache  120  in disc  112 , generating another file version to be saved causes the oldest cached version to be removed or rolled out from the cache  120 . This and subsequent file versions outputted from cache  120  in disc  112  are then stored using a time based file protection mode  114 . As described hereinafter in further detail, these file versions will be selectively stored in an external cache location  122 , for a pre-specified period of time and using a pre-specified cache strategy.  FIG. 1  shows cache  122  contained in an external drive  116 , although the cache  122  could be contained in a remote file or WebDav Web-server  118 . As is known, WebDav is an abbreviation for Web-based Distributed Authoring and Versioning. 
         [0017]    In an example illustrating the embodiment of  FIG. 1 , it is determined that a maximum of 50 versions of a file  104  can be cached at protective version storage positions, for a period of 2 years. It is further determined that 20% of the maximum number, or  10  version storage positions, is to be used for revision based file protection  110 . The remainder, or 40 cache locations, will then be used for time based file protection  114 . Thus, the first 10 updated versions of the file  104 , up to 10 versions, are continuously moved to positions in recent version cache  120 , located in local disc  112 . When an 11 th  updated version is created, this version is likewise moved to the local recent version cache  120 . Therefore, the 1 st  version to be placed in the recent version cache  120 , which is now the oldest version therein, must be removed from the local cache  120  to make room for the 11 th  version. Accordingly, the 1 st  version is moved to an external time based cache  122 , located in external hard drive  116 . Thereafter, the 10 most recent versions or revisions of the file  104  will always be retained at the recent version cache  120 , usefully located at disc  112 . 
         [0018]    As additional versions of the file  104  are created and moved to the most recent cache  120 , an equal number of older versions are moved from such cache location to join the 1 st  version at external time based cache location  122 . In a useful embodiment of the invention, when the cache location  122  reaches its maximum allowed capacity of 40 versions, a pre-specified cache strategy is implemented, such as by operation of file storage manager  108 . Generally, the cache strategy will spread out or distribute the maximum number of versions allowed, for a particular file, over the time period specified for the file. The cache strategy will determine which versions to respectively retain in, and which versions to remove, from time base cache  122 , in order to realize a particular retention goal or retention policy for the file. Moreover, cache strategies may be readily adapted or designed to implement different retention procedures for different files or types of files. 
         [0019]    It is thus seen that embodiments of the invention can provide great flexibility in file retention or back up. In one example, files in the time base cache could be retained so that they are linearly distributed over the time period. This could be achieved by saving one file version in the time based cache for each of a number of equal intervals spread over the time period. However, in other examples, distribution of saved versions over the time period would be skewed, so that a greater number of newer file versions were saved, and a comparatively small number of older versions were saved. An example of this would be a logarithmic distribution, described hereinafter in further detail in connection with  FIG. 2 . On the other hand, distribution could be skewed over the time period so that comparatively more older versions were saved than newer versions. This might be done, for example, if older versions of the file had been modified much more frequently than newer versions. 
         [0020]    Cache strategies, and decisions to retain particular file versions in the time based cache, can be further influenced by factors such as the frequency with which changes are made to a file, and the comparative importance of a file. It may also be desirable to use length of a file document as a factor, if different versions have significantly different lengths. Thus, a shorter version could be saved rather than the longer version, in order to save storage space. However, it is to emphasized that within the scope of the invention, numerous criteria and considerations, in addition to those disclosed herein, could be used in designing the cache strategy for a particular file. Accordingly, embodiments of the invention are not limited to the examples set forth above. 
         [0021]    If a version is retained in the time based cache until it reaches the end of the time period, from the date of its creation, such retained version will then generally expire. 
         [0022]    In a further example of a linear arrangement, a succession of intervals of equal time length are defined, such as intervals comprising successive daily, weekly, or monthly periods. At the end of a particular linear interval the most recent version, of all versions received or otherwise available at external cache  122  during the particular interval, is saved. 
         [0023]    It will, of course, be appreciated that in other embodiments of the invention, file versions stored according to both the revision and time based procedures can all be stored locally, or can all be stored at the same or different external locations. Moreover, in some embodiments, instead of providing a specified maximum number of versions that can be stored, a maximum amount of storage space or capacity would be specified. Percentages of the storage space would be allocated to both recent version cache storage, and time based cache storage, respectively. The actual numbers of file versions that could be stored would then depend on the size length of respective versions. 
         [0024]    For many types of files, it will typically be the case that a difference of, for example, 5 days between file versions will be much more important for files stored the previous month, than for files that were stored more than a year previously. For files of such types, it could be preferable to have a cache strategy that uses a logarithmic relationship in selecting intervals for the time interval based storage, rather than a linear relationship as discussed above. As used herein, the term “logarithmic relationship” is used to mean a succession of intervals for storing file versions, wherein intervals become longer, or shorter, over time. 
         [0025]    Referring to  FIG. 2 , there is shown a time scale depicting a logarithmic arrangement or strategy for caching file versions over logarithmic time intervals, that increase in length over time. More particularly,  FIG. 2  shows that file versions received at external time based cache  122  in  FIG. 1  are stored for a one week period  202 , during time intervals of one day in duration. During the following period  204 , which is of one month duration, successive version storage intervals are each two days in length. A third period  206  has a duration of six months, and file versions are stored at one week intervals. 
         [0026]    By providing the capabilities described above, a system can be readily adapted to meet widely varying backup requirements for different types of tiles. The adaptation can be simply carried out, by enabling a user to select parameter values that would be applied to protect a particular file. These parameter values can include (1) the total period of time that file versions are to be saved; (2) the maximum or total number of versions that can be stored; and (3) the percentages used for allocating the maximum number of versions between revision based and time interval based storage. In addition, the user can select a cache strategy that will determine the types of intervals to be used for storing versions over time. The intervals could, for example, be linear or have logarithmic relationships as discussed above. 
         [0027]    As an additional feature, a user can be provided with tags for designating the relative importance of different stored file archives or single files, (e.g., Mozart.mp3) or files of a specific extension (e.g.*.mp3), or files of a specific category (e.g. music files). Usefully, the tags are selected to indicate that a particular file archive has either a high, medium or low protection priority. For example, files containing configuration parameters or financial data could have high priorities, while attachments to emails would have low priority. 
         [0028]    Examples of settings for parameter values as described above, for different types of files, are set forth in a table shown below: 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 Resource 
                   
                 No. of 
                 Time 
                   
               
               
                 Location 
                 Tag 
                 Versions 
                 Period 
                 File Types 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Local 
                 High 
                 100 
                 2 years 
                 Configuration 
               
               
                 Drives 
                 priority 
                   
                   
                 parameters, 
               
               
                   
                   
                   
                   
                 financial 
               
               
                   
                   
                   
                   
                 data 
               
               
                 Local 
                 Low 
                 1 
                 1 week 
                 Email 
               
               
                 Drives 
                 priority 
                   
                   
                 attachments 
               
               
                 Local 
                 Medium 
                 50 
                 6 months 
                 Email archive 
               
               
                 Drives 
                 priority 
               
               
                   
               
             
          
         
       
     
         [0029]    After entering file protection parameter values such as those shown into the server  106  of  FIG. 1  file storage manager  108  is operable to provide continuous data protection for the corresponding files. In addition, a further feature can be used to determine how often specific files or types of files are accessed, and the frequency with which they are changed or modified. This feature is implemented by monitoring selected files over time, in order to track the number of changes made thereto. Information furnished by this feature can then be employed to dynamically adjust parameter settings, when using embodiments of the invention to protect files. For example, if the furnished information indicates that a particular file is frequently changed and accessed, it could be decided to allocate a large number of versions for file backup. In some embodiments, a formula could be used to relate usage directly to the number of backup versions that are allocated. 
         [0030]      FIG. 3  shows principal steps for implementing an embodiment of the invention, which may for example be carried out by file storage manager  108  of server  106 .  FIG. 3  is more particularly directed to a logarithmic cache strategy as described above, only for purposes of illustration and not limitation. At step  302 , a file modification is saved, so that a new most recent (NMR) file version is created and must be backed up. Accordingly, at step  304  it is determined to store the (NMR) version in a revision based cache, such as cache  120  in computer disc  112  of  FIG. 1 . As indicated by steps  306  and  308 , this can be readily done if the revision based cache is not yet filled to the maximum number of file versions apportioned thereto. However, if the revision based cache is filled to capacity, step  310  shows that the oldest version therein must be moved to the time interval based cache, such as cache  122 , so that the (NMR) file version can he entered into the revision based cache. 
         [0031]    At step  312 , it must be determined whether the time based cache is filled to capacity. If not, the time based cache can simply continue to receive one or more versions from the revision based cache. If the time based cache becomes filled, the time cache based strategy is implemented, as shown by step  314 . As shown by step  316 , each saved version expires upon reaching the end of the time period, regardless of whether it is saved in the time based cache or the revision based cache. 
         [0032]    As an additional feature in embodiments of the invention, retrieval of saved versions is made to be seamless, with respect to both the revision based cache and the time based cache. More particularly, versions in the revision based cache will typically be referenced by means of a version number, whereas versions in the time based cache will be referenced by means of a time date stamp. Accordingly, a mechanism is included that is responsive to requests for version retrieval using either type of reference. If a request is submitted to retrieve a particular numbered version, the time based cache will be searched as well as the revision based cache, in order to locate and retrieve the desired version. Similarly, if a retrieval request identifies a version by its time of creation, the revision based cache as well as the time based cache will be searched, in order to locate such version. 
         [0033]    In an example illustrating this capability, it is assumed that the revision based cache stores the last 10 file versions, which in fact extend back over the last 6 months. Also, versions 12, 14, 16, and 18, which extend back over the last two years, are stored in the time based cache. If a user submits a request to retrieve file version 8, clearly this would come from the revision based cache. However, if the request was for version 14, the mechanism would still locate and retrieve such version, since the mechanism is configured to search both caches for a version number. 
         [0034]    Similarly, if a user submits a request to retrieve a version created 1.5 years ago (which was version 16), such version would be located and retrieved from the time based cache. If the request was for a version created 3 months ago (which was version 9), the mechanism would locate and retrieve this version from the revision based cache, since the mechanism is configured to search both caches by date and time stamp. 
         [0035]    Referring to  FIG. 4 , there is shown a block diagram of a data processing system  400  in which aspects of the present invention may be implemented. More particularly, data processing system  400  is an example of a computer which may be adapted for use as server  106  in  FIG. 1 , to implement file storage manager  108 , and in which computer usable code or instructions for implementing processes for embodiments of the present invention may be located. System  400  employs a peripheral component interconnect (PCI) local bus architecture, although other bus architectures, such as Micro Channel and ISA, may alternatively be used. 
         [0036]    Processor  402  and main memory  404  are connected to PSI local bus  406  through PCI bridge  408 . PCI bridge  408  may also include an integrated memory controller and cache memory for processor  402 . Additional connections to PCI local bus  406  may be made through direct component interconnection or through add-in boards. In the depicted example, local area network (LAN) adapter  410 , SCSI host bus adapter  412 , and expansion bus interface  414  are connected to PCI local bus  406  by direct component connection. Audio adapter  416 , graphics adapter  418 , and audio/video adapter (A/V)  434  are connected to PCI local bus  406  by add-in boards inserted into expansion slots. Expansion bus interface  414  provides a connection for a keyboard and mouse adapter  420 , modem  422 , and additional memory  424 . 
         [0037]    In the depicted example, SCSI host bus adapter  412  provides a connection for hard disk drive  426 , tape drive  428 , CD-ROM drive  430 , and digital video disc read only memory drive (DVD-ROM)  432 . Typical PCI local bus implementations will support three or four PCI expansion slots or add-in connectors. 
         [0038]    An operating system runs on processor  402  and is used to coordinate and provide control of various components within system  400  of  FIG. 4 . The operating system may be a commercially available operating system, such as OS/2, which is available from International Business Machines Corporation. 
         [0039]    Those of ordinary skill in the art will appreciate that the hardware in  FIG. 4  may vary depending on the implementation. The depicted example is not meant to imply architectural limitations with respect to the present invention. For example, the processes of the present invention may be applied to multiprocessor data processing systems. 
         [0040]    The invention can take the form of an entirely software embodiment or an embodiment containing both hardware and software elements. In a preferred embodiment, the invention is implemented in software, which includes but is not limited to firmware, resident software, microcode, etc. 
         [0041]    Furthermore, the invention can take the form of a computer program product accessible from a computer-usable or computer-readable medium providing program code for use by or in connection with a computer or any instruction execution system. For the purposes of this description, a computer-usable or computer readable medium can be any tangible apparatus that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. 
         [0042]    The medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device) or a propagation medium. Examples of a computer-readable medium include a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk and an optical disk. Current examples of optical disks include compact disk-read only memory (CD-ROM), compact disk-read/write (CD-R/W) and DVD. 
         [0043]    A data processing system suitable for storing and/or executing program code will include at least one processor coupled directly or indirectly to memory elements through a system bus. The memory elements can include local memory employed during actual execution of the program code, bulk storage, and cache memories which provide temporary storage of at least some program code in order to reduce the number of times code must be retrieved from bulk storage during execution. 
         [0044]    Input/output or I/O devices (including but not limited to keyboards, displays, pointing devices, etc.) can be coupled to the system either directly or through intervening I/O controllers. 
         [0045]    Network adapters may also be coupled to the system to enable the data processing system to become coupled to other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modem and Ethernet cards are just a few of the currently available types of network adapters. 
         [0046]    The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.