Abstract:
Data Protection on computer data is to insure data availability. The mission critical data has been chronically stored and labeled with version, distinguished in time of stored. In order to save storage of a backup medium, one full backup is stored and then is followed by many differential or incremental backups. The disclosed employs a Direct Access Storage Device (DASD or disk) as a backup medium. Disk provides a memory model with (1) random access attribute and (2) flat address space. Therefore data restoration for a given version can be achieved by an intelligent backup disk device rather than by a backup server. Intelligent backup disk device compares backup data between different versions and eliminates redundant backup data in later version. Presently backup server performs all data protection functions that include data backup and data restoration. An intelligent primary disk device, where the primary data resides, is capable to record all write operations on a write journal continuously between the previous backup and the ensuing backup. Once a backup is requested, the primary intelligent disk device retrieves write data from its disk medium and transfers the write data along with the write journal to the intelligent backup disk device where the second copy is stored. The intelligent primary disk device and the intelligent backup disk device concertedly perform data protection functions. Furthermore, these data protection functions can be located at a SAN (Storage Area network) switch. The switch becomes the center of data protection in networked computer configuration.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to system and method to perform computer data backup and restoration and, more particularly to use Direct Access Storage Device (DASD) as a backup medium for computer data backup and restoration.  
       DESCRIPTION OF THE RELATED ART  
       [0002]     Making backup copies of important computer data to another medium is an imperative task. The computer primary data is largely stored in DASD device (Direct Access Storage Device or disk for short). Disk provides fast access for data and has characteristic of no volatile memory. There are reasons to back up computer disk data (disk image or files). One of reasons is to prevent data loss from disk hardware failure. Even the disk technology advances; the probability of disk hardware failure cannot be ignored. The second reason is to recover the disk data when a disastrous event happens at the surrounding of the computer disk and the computer disk can render not operational in the event. The third reason is to retrieve the last backup version of data in case that computer user requests to do so. The forth reason is to keep different versions of the same files as time progresses. There are requirements for computer users to retrieve files chronologically.  
         [0003]     Data Protection on computer data is to insure data availability. Data protection hereto is to backup computer data and to restore the user data upon request. There can be many versions, distinguished in time of stored, of the same disk data (disk image or files). The common computer systems typically include one or many storage devices. The storage devices are disk devices, tape drives, optical drives, etc. The enterprise systems employ disk arrays, automated tape libraries, optical drives, etc. There is at least one data backup server that executes storage management software to perform data backup and data restoration for computer system. The modern computer systems adopt network architecture; general-purpose server, backup server, disk arrays, and automated tape library are communicating through a computer network.  FIG. 1  shows a modern computer system that is based on network architecture.  
         [0004]     Backup server performs data protection functions. There are three data backup methods (i.e. full backup, differential backup and incremental backup) and two backup techniques (i.e. image backup technique, and file-by-file backup technique) that are commonly adopted.  
         [0005]     The file-by-file technique in full backup is a very time consuming task due to file allocations on the physical sectors of the disk are not sequential. There are too many recording head movements and too many wastes in disk rotations. The file system involving in file open and disk reading makes response time worse. In many occasions, even the backup tape drive that employs speed-matching buffer has to stop and re-start the tape recording. The file-by-file full backup for a network storage takes hours. However differential backup (backing up the differences from the time of the last full backup to this moment) or incremental backup (backing up the differences from the last backup (either full backup or earlier incremental backup) to this moment) can be easily performed due to that a ratio of updated files to total files in a disk volume is relatively low. A common practice is to perform full backup once a week and incremental or differential backup once per day. Full backups still need to be performed fairly regularly, because restoring the file contents from a full backup and a large set of incremental backups can be very time consuming. It is also true for differential backup because the cumulative backup data is growing rapidly as time progresses.  
         [0006]     The other technique, image backup technique, backs up disk partition images of a disk. Image full backup takes advantage of disk sequential read operations and solves the problem of file-by-file full backup. A drawback of image backup is requiring an equal or greater storage space in the backup medium than the real data in the disk that to be backed up. There is a waste in the backup medium if the disk utilization rate is low. Another disadvantage of traditional image backup is not supporting differential backup or incremental backup. The most operating systems maintain an archive bit in the file to indicate whether the file has been updated or not. Application software can figure out the physical location of the updated file but does not have knowledge to trace back other components that link the updated file to the rest of partition image in order to maintain full disk partition image. Therefore, differential or incremental backup cannot be done in image backup technique.  
         [0007]     In U.S Pat. No 5,907,672, John E. G. Matze et al disclose System for backing up computer disk volumes. Matze et al teach a method to perform an incremental backup by using a resident software module, that is running all the time in server platform, to monitor which parts of the disk volume have been updated. This allows incremental backup to take place only updated parts of the disk partition. Their technique only applies to systems that execute backup software in server platforms. This also impacts system performance.  
         [0008]     In U.S Pat. No. 6,542,975, Evers D. L. et al disclose Method and system for backing up data over a plurality of volumes. Evers D. L. et al teach a method to replicate a disk partition by copying many data chunks to a backup medium. Each data chunk associates with one data chunk descriptor that specifies the location of data in the partition image. Restoring partition image is to move the stored data chunks to the right locations of a temporary storage. This method only applies to full backup of a disk partition and is not applicable to incremental backup.  
         [0009]     IBM&#39;s Tivoli Storage Manager organizes backup storage with hierarchical structure. The Storage Manager moves backup data from one storage hierarchy level to other. The function is used to cache backup data onto a disk before moving the data to tape cartridges. The management database, that tracks relationship between locations of backup data on the backup medium and locations of backed up data on the originating disk partition, is stored within the backup server&#39;s on-line storage. Tivoli Storage Manager or other commercial storage management software generates a lot of network traffic and do not have centralized repository for management database and backup data.  
         [0010]      FIG. 2  shows network traffic for a modern computer system that employs a cache disk for data backup.  
         [0011]     In any backup techniques, either image technique or file-by-file technique, there are many redundant backup data stored on backup disk device. Without management database and backup data stored at a centralized repository, tasks to reduce the redundant backup data are slow and snarls network traffic. An intelligent apparatus, that is devised to eliminate redundant backup data in a very efficient way, will be addressed in the present invention.  
         [0012]     The deficiencies are clearly felt in the art and are resolved by this invention in the manner described below.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention provides methods and systems for backing up and restoring computer data to and from a backup disk device. The goals of the present invention are (1) eliminating performance degradation from resident software module that monitors image update at all time in image backup technique (2) resolving lacking of incremental backup supports from image backup technique or data chunk backup in the prior art (3) resolving lacking of centralized repository for backup data and management database (4) reducing redundant backup data in backup medium (5) significantly alleviating network traffic during data backup and data restoration (6) lowering overall cost by adopting new methods and systems.  
         [0014]     The systems in this invention employ disk device as the backup medium. As present time, cost per gigabyte storage for disk drive and tape cartridge are comparable. Disk device offers higher data transfer rate, random access attribute, and flat memory space. Backup disk device maintains management database, the database that tracks locations of backup data on its medium and locations of backed up data on the primary disk device, as well as stores backup data. With availability of management database and backup data, the processor in the backup disk device can restore the stored disk partition image in image backup technique. The restored disk image can be mounted as a read-only volume directly from the backup disk device. The processor in the backup disk device also can reduce or eliminate redundant backup data in backup disk device in either image backup technique or file-by-file backup technique. The backup disk device, that is capable to perform the above functions, is called intelligent backup disk device hereto.  
         [0015]     A disk device, whose data to be stored onto a backup medium, is a primary disk device. Primary disk device is continuously maintaining a write journal, collections of write operations. A primary disk device, that is capable of transferring backup identification, write record, and backup data to a backup medium, is called intelligent primary disk device. Write record is a form of write journal at time of stored. The intelligent primary disk device performs full backup or differential backup, incremental backup, and standalone backup upon request.  
         [0016]     With intelligent primary disk device and intelligent backup disk device, roles of backup server, functions of storage management software, and network traffic in performing storage management are drastically reduced. The overall cost to perform date protection is also lowered.  
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0017]      FIG. 1  shows a modern computer system that is based on network architecture.  
         [0018]      FIG. 2  shows network traffic for a modern computer system that employs a cache disk for data backup.  
         [0019]      FIG. 3  shows an exemplary computer system including general-purpose server, management station, intelligent primary disk device, and intelligent backup disk device.  
         [0020]      FIG. 4  shows an exemplary computer system including general-purpose server, management station, local disk storage pertained to management station, intelligent primary storage controller, primary disk medium, intelligent backup storage controller, and backup disk medium.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]     With intelligent primary disk device and intelligent backup disk device, roles of backup server and functions of storage management software are drastically reduced. In fact, a personal computer (PC) can replace backup server and the PC is the management station to initiate backup operation.  
         [0022]      FIG. 3  shows an exemplary computer system  100  including the general-purpose server  102 , the management station  104 , the intelligent primary disk device  106  that may have multiple LUNs (Logical Unit Numbers, LUN  2  is used for illustrative examples), and the intelligent backup disk device  108  whose capacity is much bigger that device  106 .  
         [0023]     The first illustrative example is for a configuration having single partition on LUN  2  of device  106 . The management station  104  issues a backup identification command along with a backup identification construct to the intelligent primary disk device  106 . The management station  104  also issues a backup identification command along with a backup identification construct to the intelligent backup disk device  108 . This signals the birth of backup session. The backup identification construct contains (1) Target identification—the unique identification of the device  106 , (2) Logical Unit Number—LUN  2 , (3) scope of backup—from LBA (logical Block Address)  0  to maximum LBA of LUN  2  in the device  106 , and (4) granular unit of backup data in sectors—is a user&#39;s choice (one sector or multiple sectors). The communication between management station  104  and device  106  and the communication between management station  104  and device  108  can be through either in-band connection (normal data exchange path) or out-band connection.  
         [0024]     Next step is to perform a full backup. The management station  104  issues a backup command along with a full backup construct to the device  106 . The full backup construct contains (1) Target identification, (2) LUN number, (3) scope of backup (4) version—a unique number or time of storing this backup data, (5) package type—full backup package type (6) write record—describe how many sectors in the device  106  have to be transferred to the device  108  and locations of those sectors in the device  106 . The device  106  processes this command and transfers the above information, item (1) through item (6) of the full backup construct, and the backup data, the item (7), to the device  108 .  
         [0025]     The write record contains (1) write record header and (2) write descriptive block instances.  
         [0026]     The write record header contains (1) number of write descriptive block instances—one instance of write descriptive block for this illustrative example and (2) total number of backup sectors in the write record—capacity in sector of the LUN  2  for this illustrative example.  
         [0027]     The write descriptive block includes (1) starting LBA of backup—zero (the first LBA of LUN 2 ), (2) ending LBA of backup—maximum LBA of the LUN  2 , (3) number of backup sectors in the write descriptive block—capacity in sector of the LUN  2 , (4) granularity of bit map—64 sectors (user&#39;s choice), and (5) backup bit map—omitted for this illustrative example. The meaning of the backup bit map will be explained in a later paragraph.  
         [0028]     In this illustrative example, the first example of the present invention, the full backup is to copy the whole image of the LUN  2  of device  106  to the device  108 . Device  106 , upon receiving the backup command from management station  104 , sends the full backup construct and data of full volume of LUN2 of device  106  to device  108 .  
         [0029]     In the second illustrative example, the management station  104  examines the FAT (File Allocation Table) table in the LUN  2  and finds that the first 1000 clusters are used and the rest of capacity is unused. Cluster is the smallest recording unit in a file system.  64  sectors per cluster is for this illustrative example. The differences between the first illustrative example and the second illustrative example are (1) content of the write record and (2) backup data—every sector in the LUN  2  has to be backed up in the first illustrated example versus 64,000 (64×1000) sectors of data have to be backed up in the second illustrated example.  
         [0030]     The write record header in the second illustrative example contains (1) number of write descriptive block instances—one for this illustrative example and (2) total number of backup sectors in the write record—64,000 sectors.  
         [0031]     The write descriptive block includes (1) starting LBA of backup—zero, (2) ending LBA of backup—63,999, (3) number of backup sectors in the write descriptive block—64,000, (4) granularity of bit map—64 (size of FAT&#39;s cluster in sectors), and (5) backup bit map—omitted for this illustrative example.  
         [0032]     The second illustrative example has advantage in saving storage space of the device  108  over the first illustrative example. Storing unused sectors is irrelevant. Device  106 , upon receiving the backup command from management station  104 , sends the full backup construct and data of 64,000 sectors of LUN2 of device  106  to device  108 . The full backup construct in the second illustrative example contains (1) Target (Device  106 ) Identification, (2) Logic Unit Number—LUN  2 , (3) scope of backup—from LBA  0  to maximum LBA of LUN  2 , (4) version—a unique number or time of storing this backup data, (5) package type—full backup package type (6) write record: (6a) write record header: (6aa) number of write descriptive block instances—one, (6ab) total number of backup—64,000 sectors; (6b) write descriptive block: (6ba) starting LBA of backup—zero, (6bb) ending LBA of backup—63,999, (6bc) number of backup sectors in the write descriptive block—64,000, (6bd) granularity of bit map—64, (6be) backup bit map—omitted for this illustrative example.  
         [0033]     In the third illustrative example, the management station  104  examines the FAT table in the LUN  2  and finds that the first 980 clusters and even number of clusters from cluster 40000 to cluster 40039 are used. The total number of used clusters is 1000. The difference between the third illustrative example and the second illustrative example is in the content of write record.  
         [0034]     The write record header in the third illustrative example contains (1) number of write descriptive block instances—two for this illustrative example and (2) total number of backup sectors in the write record—64,000 sectors, the same as in the second illustrative example.  
         [0035]     The first write descriptive block includes (1) starting LBA of backup—zero, (2) ending LBA of backup—((980×64)−1=) 62,719, (3) number of backup sectors in the write descriptive block—(980×64=) 62,720, (4) granularity of bit map—64, and (5) backup bit map—omitted for this illustrative example.  
         [0036]     The second write descriptive block includes (1) starting LBA of backup—(40000×64=) 2,560,000, (2) ending LBA of backup—((40040×64)−1=) 2,562,559, (3) number of backup sectors in the write descriptive block—(20×64=) 1280, (4) granularity of bit map—64, and (5) backup bit map—40 bits (10101010, 10101010, 10101010, 10101010, 10101010 in bitmap). The backup bit map traverses from cluster 40000 to 40039. Each bit represents one cluster. Binary-one value means the cluster is used. Binary-zero value means the cluster is unused. For simplicity and saving storage space, a backup bit map is omitted if all bit positions of the backup bit map contains only binary-one value. In other words, the omission of the backup bit map in a write descriptive block means that all sectors in the region from the starting LBA of backup to the ending LBA of backup of the write descriptive block are used.  
         [0037]     The third illustrative example demonstrates a flexibility of write record in the case that plurality (very likely) occurs on the image of the LUN.  
         [0038]     The third illustrative example also has advantage in saving storage space of the device  108  over the first illustrative example. Storing unused sectors is irrelevant. Device  106 , upon receiving the backup command from management station  104 , sends the full backup construct and data of 64,000 sectors of LUN 2  of device  106  to device  108 . The full backup construct in the third illustrative example contains (1) Target (Device  106 ) Identification, (2) Logic Unit Number—LUN  2 , (3) scope of backup—from LBA  0  to maximum LBA of LUN  2 , (4) version—a unique number or time of storing this backup data, (5) package type—full backup package type (6) write record: (6a) write record header: (6aa) number of write descriptive block instances—two, (6ab) total number of backup—64,000 sectors; (6b) write descriptive block  1 : (6ba) starting LBA of backup—zero, (6bb) ending LBA of backup—62,719, (6bc) number of backup sectors in the write descriptive block—62,720, (6bd) granularity of bit map—64, (6be) backup bit map—omitted for the write descriptive block  1 ; (6c) write descriptive block  2 : (6ca) starting LBA of backup—2,560,000, (6cb) ending LBA of backup—2,562,559, (6cc) number of backup sectors in the write descriptive block—1,280, (6cd) granularity of bit map—64, (6ce) backup bit map—(1010101010101010101010101010101010101010) for the write descriptive block  2 .  
         [0039]     In the fourth illustrative example, there are two disk partitions on the LUN. The image of the LUN contains disk partition table, the first partition, and the second partition. The management station  104  makes three backup identification constructs for the LUN. The three backup identification constructs contain same information of (1) Target identification (2) Logical Unit Number. Each backup identification construct has its own backup scope, starting LBA of backup scope and ending LBA of backup scope, and its own granular unit of backup data in sectors. These three backup scopes cover the whole image of the LUN  2  and cannot be overlapped. The management station  104  has to establish three backup sessions individually.  
         [0040]     The device  106  processes a full backup command and transfers a full backup package to the device  108 . Full backup package includes (1) Target identification, (2) LUN number, (3) scope of backup, (4) version—a unique number or time of storing this backup data, (5) package type—full backup package type (6) write record (7) backup data that is read from the medium of the LUN  2  of the device  106 . The device  106  and the device  108  are working on LBA (sector) basis and have no knowledge of FAT or cluster size.  
         [0041]     In the fifth illustrative example, the management station  104  issues a differential backup command along with a backup identification construct to the device  106 . The device  106  has implemented a write journal. The device  106  resets the write journal when it completes a full backup and is recording every write operation on the write journal since the last full backup. Once a differential backup is requested to the device  106 , the device  106  generates a write record based on the information on the write journal. The device  106  assembles a differential backup package and sends the differential backup package to the device  108 . The differential backup package contains (1) Target identification, (2) LUN number, (3) scope of backup (4) version—a unique number or time of storing this backup data, (5) package type—differential backup package type, (6) the write record, and (7) backup data—the data that has been updated since the last full backup. The data is read from the medium of LUN  2  of device  106 . Besides the management station  104  issues a differential backup command, a pre-set timer (e.g. one event per day) or a pre-set policy (e.g. reach the threshold of write operations) in the device  106  can also issue differential backup requests internally.  
         [0042]     In the fifth illustrative example, the device  108  receives the full backup package and the differential backup package. The device  108  stores the backup data and maintains relationship between locations of backup data on the device  108  and locations of backed up data on the device  106  in accordance to the information in the backup package into the management database. The device  108  repeats the same task for the full backup package and the differential backup package. If data restoration is requested, the device  108  reconstructs a versioned (time of stored) image of disk partition based on the information in management database and backup data. The management station  104  mounts a drive that represents a version of saved partition image.  
         [0043]     The device  108  performs redundant backup data elimination. The device  108  traverses and compares each granular unit of the backup data in the write descriptive blocks of the differential backup package and the backup data in the earlier full backup package. If comparison yields equal result, the backup data of that granular unit in the differential backup package is deemed void. The feature of the redundant backup data elimination saves the device  108 &#39;s storage and saves the data entry of the management database. Device  106  maintains write journal, that records the write operations have been done on the medium, but does not know whether the new data on the medium differs from old data on the medium.  
         [0044]     Redundant backup data elimination can also be taken place after completing updating the management database upon receiving differential backup package. The device  108  traverses the new entries, which based on the newly incoming differential backup package, and compares the new backup data against the earlier backup data. If comparison yields equal result, the granular unit of new backup data and new entry to management database are eliminated.  
         [0045]     The management database in the device  108  is paramountly critical. Loss of management database is unacceptable. Data mirroring or other RAID (Redundant Array Inexpensive Disks) scheme is recommended to protest management database.  
         [0046]     In the sixth illustrative example, the management station  104  issues an incremental backup command along with a backup identification construct to device  106 . The device  106  has implemented a write journal. The device  106  resets the write journal when it completes the last backup and is recording every write operation on the write journal since the last backup. Once an incremental backup is requested to the device  106 , the device  106  generates a write record based on the information on the write journal. The device  106  assembles an incremental backup package and sends the incremental backup package to the device  108 . The incremental backup package contains (1) Target identification, (2) LUN number, (3) scope of backup (4) version—a unique number or time of storing this backup data, (5) package type—incremental backup package type, (6) the write record, and (7) backup data—the data that has been updated since the last backup. The data is read from the medium of the LUN  2  of the device  106 . Besides the management station  104  issues a incremental backup command, a pre-set timer (e.g. one event per day) or a pre-set policy (e.g. reach the threshold of write operations) in the device  106  can also issue incremental backup requests internally  
         [0047]     In the sixth illustrative example, the device  108  receives the full backup package and a sequence of incremental backup packages. The device  108  stores the backup data and maintains relationship between locations of backup data on the device  108  and locations of backed up data on the device  106  in accordance to the information in the backup package into the management database. The device  108  repeats the same task for the full backup package and every incremental backup package. If data restoration is requested, the device  108  reconstructs a versioned image of disk partition based on the information in management database and backup data. The management station  104  mounts a drive that represents a version of saved partition image.  
         [0048]     The device  108  performs redundant backup data elimination. The device  108  traverses and compares each granular unit of the backup data in the write descriptive blocks of the incremental backup package and the backup data in a earlier backup package. If comparison yields equal result, the backup data of that granular unit in the incremental backup package is deemed void. The feature of the redundant backup data elimination saves the device  108 &#39;s storage and saves the data entry of the management database. Device  106  maintains write journal, that records the write operations have been done on the medium, but does not know whether the new data on the medium differs from old data on the medium.  
         [0049]     Redundant backup data elimination can also be taken place after completing updating the management database upon receiving incremental backup package. The device  108  traverses the new entries, which based on the newly incoming incremental backup package, and compares the new backup data against the earlier backup data. If comparison yields equal result, the granular unit of new backup data and new entry to management database are eliminated.  
         [0050]     The management database in the device  108  is critical. Loss of management database is unacceptable. Data mirroring or other RAID scheme is recommended to protest management database.  
         [0051]      FIG. 4  shows an exemplary computer system  200  including the general-purpose server  202 , the management station  204 , the local disk storage  212  pertained to the management station  204 , the intelligent primary storage controller  210 , the primary disk medium  206  that having multiple LUN (LUN  2  is used for illustrative examples), the intelligent backup storage controller device  214 , and the backup disk medium  208  whose capacity is much bigger that device  206  or storage  212 .  
         [0052]     In the seventh illustrative example, the intelligent storage controller  210  can perform the functions of device  106  in  FIG. 3 . The intelligent primary storage controller  210  is maintaining the write journal, reads backup data from the device  206 , and produces backup packages (full backup type or differential backup type or incremental backup type) upon requests. The intelligent storage controller  210  then transfers the backup packages to the device  214 . The device  214  stores backup data onto device  208 . The device  214  records locations of backup data that is stored at device  208  and locations of backed up data that is resided at the device  206  to management database. The management database is also stored at the device  208 . The intelligent backup storage controller  214  reconstructs the stored image upon request.  
         [0053]     The device  214  performs redundant backup data elimination. The device  108  traverses and compares each granular unit of the backup data in the write descriptive blocks of the differential backup package and the backup data in the earlier full backup package. If comparison yields equal result, the backup data of that granular unit in the differential backup package is deemed void. The feature of the redundant backup data elimination saves the device  208 &#39;s storage and saves the data entry of the management database. Device  210  maintains write journal, that records the write operations have been done on the medium, but does not know whether the new data on the medium differs from old data on the medium.  
         [0054]     The device  214  also performs redundant backup data elimination for the incremental backup packages. Data mirroring or other RAID scheme is recommended to protest management database.  
         [0055]     In the eighth illustrative example, the management station  204  produces backup packages based on a partition image of device  206  or a partition image of the storage  212 . The management station  204  sends the backup packages to the device  214 . The functions of device  214  have been stated in the above paragraphs  
         [0056]     Furthermore the functions of the intelligent primary storage controller can be implemented in a SAN (Storage Area Network) switch. The switch becomes the intelligent primary storage switch. The functions of the intelligent backup storage controller can be implemented in a SAN switch. The switch port becomes the intelligent backup storage switch.  
         [0057]     The functions of both intelligent primary storage controller and intelligent backup storage controller can be implemented in a SAN switch. The switch becomes the data protection storage switch.  
         [0058]     The management station  104  of system  100  or the management station  204  of system  200  or a backup server map performs Object Backup. Object is a file or a collection of files or a bunch of data. One object can be divided into one or many elements. Each element can be different construct. Backup is done via full backup package, differential backup package, or incremental backup package. Backup data of differential backup package or incremental backup package can be one or many elements (partial or whole) of the object. Full backup package contains whole object. Backup package has its identification that contains version number. The device  108  or the device  214  maintains the management database to track versions and backup data that are pertinent to an object. The redundant backup data elimination can be performed in each element of the object or in a pre-defined granular unit, which is one sector or multiple sectors. Data mirroring or other RAID feature can be used to prevent management database from data loss.  
         [0059]     Clearly, other embodiments and modifications of the present invention will occur readily to those of ordinary skill in the art in view of these teachings. Therefore, this invention is to be limited only by the following claims, which includes all such embodiments and modifications when viewed with conjunction with the above illustrative examples and accompanying figures.