Method and system of incremental computer archive storage

Abstract: The method directs a computer system to incrementally archive primary storage to archive storage based on partitions. The primary storage is divided into a plurality of partitions 201, 202, where at least one of the partitions contains information. The method includes the steps of receiving an incremental archive request from user controls and, in response, storing in the archive storage a copy of the information in each partition that has been modified since the last archive, if any.

Description: The present invention relates to a technique for providing incremental storage archive for computers using minimal archive storage space. Many computer systems employ a conventional archiving scheme to back up one or more disks. This archiving scheme writes a copy of an entire file to magnetic tape each time a user modifies and archives that file. If subsequent modifications are made to the file and the user again desires to archive it, the archiving scheme appends the entire file to the previously archived file on tape. This archiving scheme presents disadvantages and limitations. First, even if the user makes the smallest modification to a file, the archiving scheme writes the entire file to tape when the user archives it. Therefore, this archiving scheme requires substantial amounts of time to archive large files. Second, because this archiving scheme appends each archived file to the end of the previously archived file, additional amounts of tape are continuously required. EP-A 0332210 discloses a backup control system in which renewed (modified) data parts in a first memory are copied to a second memory. A control memory is used to indicate those portions of the first memory that have been renewed. EP-A 0541281 discloses an incremental backup system in which only those blocks of a file or disk partition which have been modified from corresponding earlier blocks are backed up. Such modification is detected when a signature (calculated from a cyclic redundancy code) for the block is different from a signature for the earlier version of the block. Accordingly, the invention provides a method as defined in the appended claims for incrementally archiving primary storage in a computer system to archive storage. The invention also provides a computer system as defined in the appended claims including means for incrementally archiving primary storage to archive storage. Viewed from another aspect, the invention provides a method as defined in the appended claims for directing a computer system to incrementally archive primary storage to archive storage, the primary storage being divided into a plurality of partitions, at least one of the partitions having contents stored therein, comprising the steps of: receiving an incremental archive request from user controls; and storing a copy, in the archive storage, of the contents of each partition that has been modified. Thus a computer-implemented method can direct a computer system to incrementally archive primary storage to archive storage based on partitions. The primary storage is divided into a plurality of partitions, where at least one of the partitions contains information. The method includes the steps of receiving an incremental archive request from user controls and, in response, storing in the archive storage a copy of the information in each partition that has been modified since the last archive, if any. Such an archiving scheme addresses the requirements for an archive scheme that is much faster than conventional archiving schemes and requires no additional tape. Such an archiving system does not completely rewrite a file each time a modification is made, but rather only rewrites or archives the modified sections of that file. A preferred embodiment of the invention will now be described in detail by way of example only with reference to the following drawings: Fig. 1 illustrates schematically the hardware configuration of a typical computer system; Fig. 2 illustrates a partition archive status data structure for tracking the status of disk partitions and a partition map data structure for correlating the physical location on the archive storage media with the physical partitions on the disk; Fig. 3 illustrates how a utility manages and tracks modifications to physical partitions; Fig. 4 is a flow diagram for implementing an incremental backup; Fig. 5 is a flow diagram for implementing an archive request; and Fig. 6 is a flow diagram for implementing a full backup. The preferred embodiment of the invention comprises a computer, such as a laptop computer or workstation having a hardware configuration such as illustrated in Fig. 1, controlled by software stored in the computer memory to implement a method for archiving hard disk storage. In Fig. 1, workstation 100 includes any suitable central processing unit 10, such as the PowerPC 601 (from IBM Corporation), and a number of other units interconnected via system bus 12. Illustratively, workstation 100 includes random access memory (RAM) 14, read only memory (ROM) 16, non-volatile RAM (NVRAM) 32, display adapter 36 for connecting system bus 12 to display device 38, and I/O adapter 18 for connecting peripheral devices (e.g. hard disks, read/write optical disks, CD-ROMs, and tape drives 20) to system bus 12. Workstation 100 further includes user interface adapter 22 for connecting user controls, such as keyboard 24, mouse 26, speaker 28, and a microphone, a touch screen device and/or other user interface devices (not shown), to system bus 12. Communication adapter 34 connects workstation 100 to a data processing network. Any suitable operating system (OS) may be implemented on the workstation 100; in the preferred embodiment, the workstation 100 supports the AIX operating system (from IBM Corporation). The workstation 100 includes an archive medium for retaining copies of the information stored on the hard disk. In the preferred embodiment, the archive medium is provided by tape drives 20, but any suitable type of storage media could be used to retain the copies, such as a write/read optical disk. In the preferred embodiment there is a utility, which may be incorporated into the OS, provided on any suitable computer-readable media, such as RAM 14, ROM 16, a magnetic diskette, magnetic tape, or optical disk (the last three being located in disk and tape drives 20). The utility controls and directs CPU to perform various tasks based on data structures and logic (described below) contained within the utility, which can be interpreted by the workstation in known fashion. The OS logically divides all primary disk storage into equally-sized partitions, called physical partitions. The user typically modifies the contents of some of those physical partitions before requesting an archive. Fig. 2 illustrates how the utility manages and tracks modifications to physical partitions. To detect whether a user has modified a physical partition, the utility examines a partition archive status array table. For example, partition archive status array 200 contains the modification status for physical partitions 201-212. Each status bit 240 indicates whether the information residing in its physical partition has been modified since the last archive operation. The utility initially sets all status bits 240 to "Archived." The utility tracks user access to each physical partition 201-212 by setting status bit 240. For example, the utility sets status bit 240 to a "1" bit to indicate "Modified", and sets status bit 240 to a "0" bit to indicate "Archived." In an incremental archive, the utility selects all physical partitions having a status bit of "Modified" (indicating that they have been modified since the last archive) and copies them to the archive medium. Therefore, during incremental archive, the utility archives only those physical partitions marked "Modified". Once the archive is accomplished, the utility resets every status bit 240 corresponding to each archived physical partition to "Archive" (indicating that those physical partitions have not been modified since the last archive operation). This type of selective archive operation prevents archiving of "empty" partitions that have not been modified. For optimal use, the utility maintains partition archive status array 200 primarily in RAM 14, while occasionally storing it to disk. Referring to Figs. 2 and 3, entries in partition map array 220 contain a mapping from one physical partition 201-212 to a corresponding physical partition 221-232 on the archive medium. Therefore, array 220 indicates exactly where the contents of each physical partition are copied on the archive media. When a physical partition is not currently used to hold valid data, such as physical partition 204, array 200 holds an invalid value for that particular partition. For example, array entry 240 indicates that partition 204 is "not mapped" and should not be considered during an incremental backup process. The utility maintains partition map array 220 on both the hard disk and archive media and updates it during archive operations or during the deletion of a physical partition from its logical volume. Fig. 4 illustrates detailed logic for implementing an incremental backup. At 400, the utility determines if an archive request has been generated by user controls. If the utility receives an archive request, control is directed to Fig. 5. If not, at 402, the utility determines if the request is a READ request. Because a READ of a physical partition does not affect its contents, the utility performs no action on array 200 or 220 when a READ occurs. Therefore, at 404, the OS performs the READ and control returns to 400. If a READ request was not received, at 406, the utility determines if the request is to delete a grouped set of physical partitions. If not, at 408, the utility performs a WRITE operation. At 410, for each physical partition that has been modified, the utility sets status bit 240 to "Modify" in partition status array 200. Control returns to 400. Returning to 406, if the request is to delete a grouped set of physical partitions, at 412, the utility reads partition map array 220 from the hard disk. At 414, the utility marks each array entry corresponding to each deleted physical partition "not mapped." At 416, the utility writes an updated partition map array 220 onto the disk and, at 418, the utility sets status bit 240 to "archived" in partition archive status array 200 for each deleted physical partition. Control returns to 400. Returning to 400, if the utility determines that the request is an archive request, control is directed to 500 in Fig. 5. At 500, the utility determines if the request is for an incremental archive. If so, at 510, the utility reads partition map array 220 from the disk. At 515, the utility reads the first status bit 240 from partition archive status array 200. At 520, the utility determines if the first status bit 240 has been set to "Modify." If not, at 525, the utility determines if there are any more status bits 240 to be read in partition archive status array 200. If so, control returns to 515, where the next status bit 240 is read. If not, control returns to 400 in Fig. 4. At 520, if the utility determines status bit 240 has been set to "modify," at 530, the utility changes the "modify" bit to an "archive" bit. At 535, the utility determines if the modified physical partition has a valid array entry in partition map array 220. If not, at 540, the utility creates an array entry for the modified physical partition in partition map array 220. If the modified physical partition does have a valid array entry in partition map array 220, at 545, the utility locates the archive partition corresponding to the modified physical partition and performs an update at that location. Control is then directed to 525 where the utility determines if there are any more status bits to read in partition archive status array 200. Returning to 500, if the utility determined that the request was not for an incremental archive but rather a full backup, control is directed to Fig. 6. In this case, the utility is not concerned with the status bit of physical partitions. At 600, the utility loads partition map array 220 from the disk into RAM and proceeds to archive every physical partition to tape that has a valid array entry. To do so, at 610, the utility reads the first array entry in partition map array 220. At 620, the utility sets status bit 240 in partition archive status array 200 corresponding to the array entry to "Archive." At 630, the utility determines if the array entry maps to a valid archive partition. Those that are marked "not mapped" indicate blank, unused, or deleted physical partitions that are no longer recognized by the system and should not be archived. If the array entry is not properly mapped, at 640, the utility determines if there are any more array entries to read from partition map array 220. If not, control returns to block 400 in Fig. 1. If so, control returns to 610, where the utility reads the next array entry. Returning to 630, if the array entry does map to a valid tape location, at 650, the utility copies the contents of the primary storage physical partition to the mapped location on the archive media and control returns to 640. Once this full archive is complete, the utility stores partition map array 220 to a reserved portion of the archive media for use when a restoration is required. The utility performs a restore operation by copying selected archive partitions from the archive media onto their corresponding primary physical partitions. Like the archive operation, the utility sorts the archive partition numbers and accesses the saved data for restoration in sequential order to minimize data access time. For an incremental restore, the utility examines partition archive status array 200 and restores only those physical partitions marked "Modified". The remaining physical partitions marked "Archived" match what was written to tape, and thus do not need any type of data restoration. When the utility copies a partition from archive to primary storage, the status bit is set to "Archived" because the archive and primary data match.

Claims: A method for incrementally archiving primary storage in a computer system (100) to archive storage, the primary storage being divided into a plurality of partitions, said system including a partition status table (200) having a plurality of entries (240), each entry indicating whether a corresponding partition has been modified since a previous archive operation, and a partition map table (220) having a plurality of array entries (221, 222), each array entry indicating a location on the archive storage where a corresponding partition is or should be stored, the method comprising, for each incremental archive operation, the steps of: scanning the entries in the partition status table, and for each entry determining if the entry indicates a modified partition; scanning the partition map array to locate the array entry corresponding to a modified partition, and determining if the located array entry indicates a valid archive partition on the archive storage; in response to determining that the located array entry indicates a valid archive partition, storing in the archive storage a copy of the contents of the partition (202, 203) that has been modified since the previous archive operation and setting the corresponding entry to an archive (non-modified) status; and in response to determining that the located array entry does not indicate a valid archive partition, creating an array entry indicating an archive partition for storing a copy of the modified partition; and storing a copy of the contents of the modified partition to the archive partition; and setting the corresponding entry to an archive (non-modified) status. A computer system (100) including means for incrementally archiving primary storage to archive storage, the primary storage being divided into a plurality of partitions, said system including a partition status table (200) having a plurality of entries (240), each entry indicating whether a corresponding partition has been modified since a previous archive operation, and a partition map table (220) having a plurality of array entries (221, 222), each array entry indicating a location on the archive storage where a corresponding partition is or should be stored, the means for incrementally archiving primary storage to archive storage comprising: means for scanning the entries in the partition status table, and for each entry determining if the entry indicates a modified partition; means for scanning the partition map array to locate the array entry corresponding to a modified partition, and for determining if the located array entry indicates a valid archive partition on the archive storage; means, responsive to determining that the located array entry indicates a valid archive partition, for storing in the archive storage a copy of the contents of the partition (202, 203) that has been modified since the previous archive operation and for setting the corresponding entry to an archive (non-modified) status; and means, responsive to determining that the located array entry does not indicate a valid archive partition, for creating an array entry indicating an archive partition for storing a copy of the modified partition; and for storing a copy of the contents of the modified partition to the archive partition; and for setting the corresponding entry to an archive (non-modified) status.

Inventors: LAHR JONATHAN E, MCBREARTY GERALD F, SHIEH JOHNNY M, TROPIANO LEONARD B, LAHR, JONATHAN E., MCBREARTY, GERALD F., SHIEH, JOHNNY M., TROPIANO, LEONARD B.
Applicants: IBM, INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1996
Main classification: G06F17
IPC codes: G06F11, G06F12, G06F17