Patent Abstract:
A data center for data backup and replication, including a pool of multiple storage units for storing a journal of I/O write commands issued at respective times, wherein the journal spans a history window of a pre-specified time length, and a journal manager for dynamically allocating more storage units for storing the journal as the journal size increases, and for dynamically releasing storage units as the journal size decreases.

Full Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to data backup and replication. 
       BACKGROUND OF THE INVENTION 
       [0002]    Data backup and replication systems create copies of enterprise data at local or remote sites. Some conventional backup and replication systems operate by tracking I/O write commands from physical or virtual servers to storage devices such as storage area network (SAN), network attached storage (NAS) and direct attached storage (DAS). Other conventional systems operate by creating clones or snapshots of enterprise data. Such systems generally save only the last snapshot or clone on disk, or several last snapshots or clones. Recent systems provide continuous data protection (CDP) by journaling write commands so at so provide any point in time data recovery. 
         [0003]    Conventional systems limit CDP capability based on disk space available to maintain a journal. Service providers define their objectives and service level agreements (SLAB) in terms of time. For CDP, the SLA generally relates to the window of time history that can be recovered. 
         [0004]    As such, a drawback with conventional data backup and replication systems is that an IT professional must be able to correctly estimate the disk space that will be required in order to maintain a desired time frame, and reserve this amount of disk space. Generally, the estimation is inaccurate and the reserved disk space is wasted. Specifically, during off-peak periods, the reserved disk space is unused, and during peak periods the disk space is not able to accommodate all of the changes and maintain the entire SLA history window. 
         [0005]    Today, enterprise infrastructures are evolving as pools of resources for on-demand use, instead of reserved pre-allocated resources. Thus it would be of advantage to provide a data backup and replication system that is flexibly adaptable to journal size requirements. 
       SUMMARY OF THE DESCRIPTION 
       [0006]    Aspects of the present invention overcome drawbacks with conventional data backup and replication systems, by leveraging a resource pool of enterprise storage units available for journaling and data replication, to adjust the size of a CDP journal on demand. Data backup and replication systems of the present invention flexibly accommodate disk space required for journaling, allocating more storage units during peak periods, and releasing storage units during off-peak periods. 
         [0007]    Further aspects of the present invention enable test journaling in parallel with production journaling, by allocating storage units devoted to test data. The storage units devoted to test data are allocated as required during a test, and are released upon completion of the test. Production data replication and protection continue in parallel with test journaling, without disruption. 
         [0008]    There is thus provided in accordance with an embodiment of the present invention a data center for data backup and replication, including a pool of multiple storage units for storing a journal of I/O write commands issued at respective times, wherein the journal spans a history window of a pre-specified time length, and a journal manager for dynamically allocating more storage units for storing the journal as the journal size increases, and for dynamically releasing storage units as the journal size decreases. 
         [0009]    There is additionally provided in accordance with an embodiment of the present invention a computer-based method for a data center, including receiving, by a computer at a sequence of times, new data to add to a journal, the journal including one or more allocated storage resources from a pool of resources, and wherein journal data is stored in the allocated storage resources and promoted from time to time to a recovery disk, determining, by the computer, if the journal already contains data for an entire pre-designated time history, additionally determining, by the computer, if the addition of the new data to the journal would cause the journal to exceed a pre-designated maximum size, further determining, by the computer, if the additional of the new data to the journal requires allocating an additional storage resource to the journal, when the further determining is affirmative, then yet further determining, by the computer, if the pool of resources has a free storage resource available, when the determining or the additionally determining or the yet further determining is affirmative, then promoting, by the computer, old time data to a recovery disk, removing, by the computer, old time data from the journal, and releasing, by the computer, one or more of the storage resources from the journal, if all of the data from the one or more storage resources was promoted to the recovery disk, when the further determining is affirmative, then allocating, by the computer, an additional storage resource to the journal, and adding, by the computer, the new data to the journal. 
         [0010]    There is further provided in accordance with an embodiment of the present invention a method for data backup and replication, including accessing a pool of multiple storage units for storing a journal of I/O write commands issued at respective times, wherein the journal spans a history window of a pre-specified time length, dynamically allocating more storage units for storing the journal as the journal size increases, and dynamically releasing storage units as the journal size decreases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present invention will be more fully understood and appreciated from the following detailed description, taken in conjunction with the drawings in which: 
           [0012]      FIG. 1  is a first simplified diagram of a data center with enhanced data replication journaling, in accordance with an embodiment of the present invention; 
           [0013]      FIG. 2  is an administrative user interface screenshot for setting data replication journal parameters, in accordance with an embodiment of the present invention; 
           [0014]      FIG. 3  is a subsequent simplified diagram of the data center, vis-à-vis the diagram shown in  FIG. 1 , in accordance with an embodiment of the present invention; and 
           [0015]      FIG. 4  is a simplified flowchart of a method for a data center, in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Aspects of the present invention relate to data backup and replication systems that flexibly allocate and release storage units required for journaling, from a resource pool of storage units, allocating more storage units during peak periods, and releasing storage units during off-peak periods. 
         [0017]    Reference is made to  FIG. 1 , which is a first simplified diagram of a data center  100  with enhanced data replication journaling, in accordance with an embodiment of the present invention. Data center  100  is used to replicate data from a protected site to a recovery site. The replicated data may be used for a failover, to ensure business continuity when the protected site is not fully functional. 
         [0018]    As shown in  FIG. 1 , protection is configured individually for different server groups, such as server group  110 A and server group  1108 . Each server group  110 A and  1108  includes one or more physical or virtual servers. Each server group  110 A and  1108  reads and writes data in one or more respective physical or virtual disks  120 A and  120 B. 
         [0019]    The recovery site includes a journal  130  and one or more recovery disks  140 . Data transfer between the protected site and the recovery site is via a wide area network (WAN)  150 . 
         [0020]    Data center  100  replicates data by intercepting write requests between server groups  110 A and  1108  and their respective disks  120 A and  120 B, transmitting the write requests to journal  130  via WAN  150 , storing the write requests as journal entries in journal  130 , and periodically promoting the write requests to recovery disk  140  by applying them to the data in recovery disk  140  and thereby updating recovery disk  140  to a more recent time. 
         [0021]    In accordance with an embodiment of the present invention, journal  130  uses a pool of storage resources as necessary, instead of using dedicated storage. The journal shown in  FIG. 1  stores a history window of 12 hours&#39; worth of data, each hour&#39;s worth of data being numbered chronologically “1”-“12” from oldest to newest. I.e., the first hour&#39;s data is labeled “1”, and the 12 th  hour&#39;s data is labeled “12”. The various individual hours&#39; worth of data are of varying sizes, as different amounts of data activity occur during different hours of the day. At the stage shown in  FIG. 1 , the data in recovery disk  140  corresponds to the zero-hour data (TIME=0). 
         [0022]    Moreover, journal  130  stores its history in data chunks  135 , each data chunk being stored in a different resource from the pool of storage resources. Data chunks  135  are labeled “A”-“E” for reference. Data chunks  135  are also of varying sizes, as the resources from the pool of resources are generally of different sizes. In general, an hour&#39;s worth of data may fit within a single data chunk  135 , or may require more than one data chunk  135 . 
         [0023]    Journal  130  is configured by an administrator to store a specified time history window of data, irrespective of space required. Journal  130  allocates and de-allocates resources from the pool of storage resources, to dynamically expand when more data chunks  135  are required and to dynamically contract when fewer data chunks  135  are required. As such, resources are freed for other applications when journal  130  requires less storage space, instead of being dedicated to the journal as in conventional journaling systems. 
         [0024]    Reference is made to  FIG. 2 , which is a screenshot of an administrative user interface  200  for setting data replication journal parameters for a protection group, such as server group  110 A, in accordance with an embodiment of the present invention. Shown in  FIG. 2  are settings  201 - 210  for specifying various protection group parameters. Setting  201  is for specifying a priority, used for determining priority for transferring data from the protection group to the recovery site, when WAN  150  has limited bandwidth and when there is more than one protection group at the protected site. Setting  202  is for specifying a recovery point objective (RPO) threshold, which is the maximum desired time lag between the latest data written at the protected site and the latest data safely replicated at the recovery site. Setting  203  is for specifying a maintenance history, which is the time window for which write commands are saved in journal  130 . E.g., if the specified maintenance history is 12 hours, as in  FIG. 1 , then data may be recovered to any checkpoint within the past 12 hours. Setting  204  is for specifying a maximum journal size. When journal  130  reaches its maximum size, older journal entries are promoted to recovery disk  140  and removed from journal  130 . Setting  205  is for specifying a test period, which is a time between tests for checking integrity of the protection group. Setting  206  is for specifying WAN compression; i.e., whether or not data is compressed at the protected site prior to being transferred via WAN  150  to the recovery site. Setting  207  is for specifying a host at the recovery site that handles the replicated data. Setting  208  is for specifying a datastore at the recovery site for storing the replicated data. Setting  209  is for specifying a test network for use during a test failover. Setting  210  is for specifying a failover network for use during an actual failover. Generally, the failover network is a network suitable for the recovery site deployment architecture. 
         [0025]    Reference is made to  FIG. 3 , which is a subsequent simplified diagram of data center  100 , vis-à-vis the diagram shown in  FIG. 1 , in accordance with an embodiment of the present invention.  FIG. 3  shows that when the journal stores a full window history of data, such as 12 hours&#39; worth of data, and newer data arrives, the oldest hour&#39;s worth of data is promoted to recovery disk  140  prior to adding the newest data. Specifically, the data labeled “1”, which is the oldest time data in journal  130 , is promoted to recovery disk  140 . I.e., the write requests in data “1” are applied to recovery disk  140 , thereby updating the contents of disk  140  from being current for TIME=0 to being current for TIME=1. Data “1” is then removed from journal  130 . Moreover, removal of data “1” frees data chunk A, which is then de-allocated so that it can be used by other applications, or reused by journal  130 . Thereafter, the new data labeled “13” is added to journal  130 , which now stores data “2” to 13″. 
         [0026]      FIG. 3  shows that that data “13” is smaller than data “1” and, as such, the space required for storing data “2” to “13” is less than the space required for storing data “1” to “12”. Moreover, journal  130  does not require as many data chunks at TIME=13 than it did at TIME=12, and non-used resources are freed at TIME=13 for use by other applications. Specifically, data chunks “B”-“E” suffice for storing data “2” to “13”, and data chunk “A” is freed up. 
         [0027]    As shown in  FIG. 2 , setting  204  enables an administrator to specify a maximum journal size. When storage of new data would cause journal  130  to exceed its maximum size, the oldest data is promoted to recovery disk  140  and removed from journal  130 , until journal  130  is able to store the new data within its size limit. In such case, journal  130  may store less than 12 hours&#39; worth of data; i.e., less than the history specified by setting  203 . 
         [0028]    Reference is made to  FIG. 4 , which is a simplified flowchart of a method  300  for a data center, in accordance with an embodiment of the present invention. At operation  310 , new data is available for journaling. At operation  320  a determination is made whether or not journal  130  already contains a complete time window history of data, such as 12 hours&#39; worth of data. If so, then at operation  330  the currently oldest time data in journal  130  is promoted to recovery disk  140  and removed from the journal. At operation  340  the oldest data chunk  135  is freed from the journal if all of the data that it stored was promoted to recovery disk  140 , and processing advances to operation  350 . If is determined at operation  320  that journal  130  does not contain a complete time window history of data, then processing advances directly from operation  320  to operation  350 . 
         [0029]    At operation  350  a determination is made whether or not addition of the new data would cause journal  130  to exceed its maximum size. If so, then processing returns to operation  330 . Otherwise, processing advance to operation  360  where a determination is made whether or not addition of the new data requires allocation of an additional data chunk  135 . If allocation of an additional data chunk is required, then at operation  370  a determination is made whether or not an additional data chunk is available from the resource pool. If an additional data chunk is not available, the processing returns to operation  330 . If an additional data chunk is available, then at operation  380  an additional data chunk is allocated to the journal and processing returns to step  370 . If it is determined at operation  360  that allocation of an additional data chunk is not required, then processing advances to operation  390  where the new data is added to the data chunks allocated to the journal. 
         [0030]    Whenever operation  340  is performed, any unused resources by journal  130  are de-allocated and freed for use by other applications. Whenever operation  380  is performed, additional resources are allocated to journal  130 . 
         [0031]    In accordance with an alternate embodiment of the present invention, allocation and de-allocation of resources for journal  130  is performed asynchronously with the actual journaling. Specifically, promotion of data from journal  130  to recovery disk  140 , allocation of resources  135 , and de-allocation of resources  135  are performed periodically, irrespective of whether or not new data has arrived for journaling. As a result, the speed of journaling new data is increased, since operations  320 - 380  of  FIG. 4  are not performed at the time of journaling the new data. In this alternate embodiment, the maximum size constraint is not enforced at all times, and instead is exceeded for short durations. 
         [0032]    The above description relates to production journaling. However, the present invention also applies to test journaling, for testing integrity of data recovery during a failover. In this regard, it is noted that prior art systems generally stop replication of production data while a test is being performed. As such, new production data is not being protected during the test. 
         [0033]    Using the present invention, journal testing is performed in parallel with production journaling, in order to avoid disruption of production replication and protection. 
         [0034]    For test journaling, data chunks  135  devoted to testing are allocated to the journal, as required for storing test data, in addition to the production data chunks  135  described hereinabove. During a test, journal test data is stored in data chunks devoted to testing and, in parallel, journal production data is stored in production data chunks. The data chunks devoted to testing are not promoted to recovery disk  140 . 
         [0035]    Upon completion of a journal test, the data chunks devoted to testing are released, and the production data continues to be journaled. 
         [0036]    In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific exemplary embodiments without departing from the broader spirit and scope of the invention as set forth in the appended claims. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.

Technology Classification (CPC): 6