Abstract:
A system is disclosed that includes a host system to issue a write command, a primary storage controller to write data to a primary volume, and a secondary storage controller to mirror the data to a secondary volume. In the event the secondary storage controller is unable to mirror the data due to a busy state, a busy signal may be sent to the primary storage controller. The primary storage controller may initiate a timer in the event it receives the busy signal, and, in the event the busy state does not end before expiration of the timer, notify the host system that the primary and secondary volumes are in a suspended state. To alter the duration of the timer, the host system may be configured to dynamically alter the duration of the timer by sending a command to the primary storage controller.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to data storage devices and more particularly to systems and methods for dynamically configuring timers used to monitor long busy states in a remote mirror and copy environment. 
         [0003]    2. Description of the Related Art 
         [0004]    In a remote mirror and copy environment, whenever a primary (i.e., source) storage controller mirrors data to a secondary (i.e., target) controller, the primary controller monitors the state of the secondary volumes that are being used to mirror the data. The primary controller may utilize a “long busy” timer to monitor the state of the secondary volumes in a peer-to-peer remote copy (PPRC) relationship. 
         [0005]    Conventionally, the long busy state timer in the primary storage controller has been hard coded to a certain value. Analysis of several critical field problems, however, has led to the discovery that the problems may have been prevented or mitigated if the long busy state timer had a different value than the hard coded value. Consequently, some customers may desire a long busy state timer that has a value greater than the hard coded value. This may reduce the likelihood that a suspended condition will occur when a secondary volume undergoes a lengthy error recovery process. Other customers, by contrast, may desire a long busy state timer with a reduced value so the suspended condition occurs more frequently. This may prevent application I/O from building up while a secondary storage controller undergoes a lengthy recovery process. 
         [0006]    Currently, the only way a customer can change the value of the long busy state timer is using a peek-and-poke capability. The peek may be used to view the current value of the long busy state timer and the poke may be used to modify the value. When microcode in the primary controller detects a poke event, the microcode may replace the default value with a user-selected value. By design, the long busy state timer value may be persistent across initial microcode loads, warmstarts, and failure conditions in the storage controller. 
         [0007]    Although a peek-and-poke process may provide a way to modify the value of the long busy state timer, it may still not be flexible enough to satisfy customer needs. Modifying the value may require user intervention and thus may be impossible to modify in real time. In addition, the peek-and-poke capability may be susceptible to errors because the timer value must normally be set in all clusters of one or more primary controllers, and the wrong variable may be poked. Poking the wrong variable may cause unpredictable behavior or even catastrophic failures in the storage system. 
         [0008]    In view of the foregoing, what is needed is a system and method to dynamically alter the value of a long busy state timer. Ideally, the system and method could be used to modify the value in real time without requiring user intervention. Similarly, the system and method would ideally enable the timer value to be dynamically modified for different applications. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available systems and methods. Accordingly, the present invention has been developed to provide improved systems and methods to dynamically alter a long busy state timer in a remote mirror and copy environment. 
         [0010]    In a first aspect of the invention, a system in accordance with the invention may include a host system to issue a write command. A primary storage controller may receive the write command and, in response, write data to a primary volume associated with the primary storage controller. A secondary storage controller may receive a copy of the data from the primary storage controller and mirror the data to a secondary volume associated with the secondary storage controller. In the event the secondary storage controller is unable to mirror the data because it is in a busy state, the secondary storage controller may send a busy signal to the primary storage controller. The primary storage controller may initiate a timer in the event it receives the busy signal. In the event the busy state does not end before expiration of the timer, the primary storage device may notify the host system that the primary and secondary volumes are in a suspended state. To alter the duration of the timer, the host system may be configured to dynamically alter the duration of the timer by sending a command to the primary storage controller. 
         [0011]    In selected embodiments, the host system may be configured to dynamically alter the timer duration for different applications running on the host system. In other embodiments, the host system may be configured to dynamically alter the duration of the timer to correspond to other timers operated by the host system. In selected embodiments, the command is configured to modify the timer duration for at least one of a single volume pair, multiple volume pairs, and all volumes in a logical subsystem. 
         [0012]    In another aspect of the invention, a method to dynamically alter a value of a long busy state timer in a remote mirror and copy environment may include issuing a write command and writing data to a primary volume in response to the write command. An attempt may be made to mirror the data to a secondary volume. In the event a busy condition exists that prevents mirroring the data to the secondary volume, a busy signal may be sent. A timer may be initiated in the event the busy signal is sent. The primary and secondary volumes may be suspended in the event the timer expires before the busy condition has ended. The method may further include dynamically altering the duration of the timer by issuing a command. 
         [0013]    The present invention provides novel systems and methods for dynamically alternating a busy state timer in a remote mirror and copy environment. The features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through use of the accompanying drawings, in which: 
           [0015]      FIG. 1  is a high-level block diagram illustrating one embodiment of a system for dynamically altering a busy state timer in a remote mirror and copy environment; 
           [0016]      FIG. 2  is a flow chart illustrating one scenario that may be encountered by the system illustrated in  FIG. 1 ; and 
           [0017]      FIG. 3  is a flow chart illustrating another scenario that may be encountered by the system illustrated in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of systems and methods in accordance with the present invention, as represented in the Figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of certain examples of presently contemplated embodiments in accordance with the invention. The presently described embodiments will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. 
         [0019]    Referring to  FIG. 1 , in selected embodiments, a system  100  in accordance with the invention may include a host system  102 , a primary storage device  104 , and a secondary storage device  106 . A host system  102  may be configured to write to the primary storage device  104 , which may include a primary storage controller  108  and one or more primary volumes  110  associated with the primary storage controller  108 . Whenever data is written to the primary storage device  104 , the data may be mirrored to a secondary storage device  106 , which may include a secondary storage controller  112  and one or more secondary volumes  114 . To keep the data in the volumes  110 ,  114  consistent, the system  100  may utilize a protocol such as Remote Mirror and Copy, Peer-to-Peer Remote Copy (PPRC), or other similar protocol. 
         [0020]    In selected embodiments, whenever a primary storage controller  108  mirrors data to the secondary controller  112 , the primary controller  108  may monitor the state of the secondary volumes  114 . In certain embodiments, the primary controller  108  may utilize a “long busy state” timer  116  to monitor the state of the secondary volumes  114 . 
         [0021]    The long busy state timer  116  may be used to monitor the state of the secondary volumes  114  if the secondary storage controller  112  has rejected a primary volume I/O with a signal indicating it is in a long busy state. A secondary storage controller  112  may go into long busy state as a result of several conditions in the secondary storage controller  112 . For example, the secondary controller  112  may return a long busy signal if it receives I/O during a warmstart or failover recovery process. In other cases, the secondary controller  112  may return a long busy signal if a disk drive module (DDM) is undergoing a recovery process. 
         [0022]    Once the primary storage controller I/O is rejected with a long busy signal, the primary storage controller  108  may send a long busy signal to the host system  102  where the I/O originated. At this point, one of two events may occur. The secondary volumes  114  may change state from long busy to no longer long busy. Alternatively, the long busy state timer  116  may expire in the primary storage controller  108 . 
         [0023]    If the secondary volumes  114  transition from long busy to no longer long busy, the secondary storage controller  112  may notify the primary storage controller  108  that it is no longer in long busy state. The primary storage controller  108  may then notify the host system  102  that the volumes (i.e., the primary and secondary volumes  110 ,  114 ) are no longer in long busy state. The host  102  may then reinitiate the I/O that was previously rejected with long busy status. 
         [0024]    Conversely, if the long busy state timer  116  expires, the primary storage controller  108  may query the secondary storage controller  112  to determine the state of the secondary volumes  114 . One of two events may occur in response to this query. The secondary storage controller  112  may respond that the secondary volumes  114  are no longer long busy or the secondary storage controller  112  may respond that the secondary volumes  114  are still in long busy state. If the secondary volumes  114  are no longer in long busy state, the primary storage controller  108  may notify the host  102  that the volume is no longer in long busy state. The host  102  may then reinitiate the I/O that was rejected with long busy status. 
         [0025]    If, on the other hand, the secondary volumes  114  are still in long busy state after the long busy state timer  116  has expired, the primary storage controller  108  may initiate its recovery process. The primary storage controller  108  may also suspend the secondary volumes  114  and report to the host  102  that the volumes (i.e., the primary and secondary volumes  110 ,  114 ) are suspended. 
         [0026]    When the host  102  has been notified that the volumes  110 ,  114  are suspended, the host  102  may invoke its recovery procedure. For example, in a count-key-data (CKD) host environment, a recovery procedure called HyperSwap may be invoked. This procedure sends a freeze command to the primary storage controller  108  and the primary storage controller  108  in turn freezes all I/O to the volume pairs in the logical subsystem associated with the suspended volume. HyperSwap will then cause the host  102  to swap to the secondary storage controller  112 . In essence, this causes the secondary storage controller  112  to become the primary storage controller  108 . 
         [0027]    The duration of the long busy state timer  116  may be controlled by a timer value  118 . Unlike the hard-coded value described previously, the timer value  118  may be modified using a command  130  (e.g., PPRC Long Busy State timer) in accordance with the invention. This command  130  may provide a way for the host system  102  to manage and control the duration of the long busy state timer  116 . 
         [0028]    Using this command  130 , a host  102  may adjust the duration of the long busy state timer  116  in real time. In selected embodiment, the command  130  may enable a host  102  to adjust the duration of the long busy state timer  116  for different applications  120 ,  122 . For example, the duration of the long busy state timer  116  may be reduced when backing up a critical database. Likewise, the duration of the long busy state timer  116  may be increased when backing up a non-critical database. 
         [0029]    In other embodiments, the command  130  may allow the host system  102  to adjust the duration of the long busy state timer  116  to correspond to one or more timers  124  of the host system  102 . For example, an IBM S/ 390  host may set the duration of the timer  116  to correspond to a Missing Interrupt Handler (MIH) timeout value or to a Geographically Dispersed Parallel Sysplex (GDPS) timer. 
         [0030]    In selected embodiments, the timer value  118  may be limited to a range of values. For example, if a command  130  attempts to set the timer duration above a maximum value  126  or below a minimum value  126 , the microcode of the primary storage controller  108  may set the timer value  118  to a maximum or minimum value  126  closest to the desired value. Alternatively, the microcode may set the timer value  118  to a default value  128  between the maximum and minimum values  126 . 
         [0031]    In selected embodiments, the command  130  may be designed to provide selection granularity. For example, a first timer value  118  may be designated for Metro Mirror applications, whereas a different timer value  118  may be designated for Global Copy applications. Similarly, in other embodiments, the command  130  may be designed so that the host system  102  may designate a timer value  118  for a single volume pair, multiple volume pairs, or all volumes in a logical subsystem. 
         [0032]    Referring to  FIG. 2 , in a first scenario, a host system  102  may begin by initializing  200  a PPRC application and initializing  202  the value of the long busy state timer  116 , such as with the default value  128 . The host  102  may then analyze  204  an application to start on the host system  102  and send  206  a command to set the long busy state timer value  118  to a value that is desired for the application. If the timer value is between the maximum and minimum values  126 , the primary storage controller may set  208  the timer value  118  to that indicated by the host  102 . If the timer value is not between the maximum and minimum values  126 , the primary storage controller may set  208  the timer value  118  to a value between the maximum and minimum values  126 , such as to the default value  128 . 
         [0033]    The host system  102  may then attempt to write  210  data to the primary storage device  104 . The primary storage device  104  may receive  212  and store  212  the data and send  214  a copy of the data to the secondary storage device  106  to mirror the data to the secondary volumes  114 . If the secondary storage device  106  is not in long busy state, the secondary storage device  106  may store  216  the data in the secondary volumes  114  and send  218  an acknowledge signal to the primary storage device  104 . The primary storage device  104  may then send  220  an acknowledge signal to the host system  102  indicating that the write operation has successfully completed. 
         [0034]    Referring to  FIG. 3 , in another scenario, the host system  102  may perform the same basic steps  200 ,  202 ,  204 ,  206 ,  208  described in association with  FIG. 2 . The host system  102  may then attempt to write  210  data to the primary storage device  104 . The primary storage device  104  may receive  212  and store  212  the data and then send  214  a copy of the data to the secondary storage device  106  to mirror the data to the secondary volumes  114 . 
         [0035]    In this scenario, the secondary storage device  106  rejects the write and responds  300  with a long busy status. The primary storage device  104  receives  302  this status information and notifies the host system  102  that the write has been rejected  304  due to long busy status. The primary storage device  104  may also initiate  306  the long busy state timer  116  at this time. If the secondary storage device  106  does not notify the primary storage device  104  that it is no longer in long busy state before the timer  116  expires, the primary storage device  104  may query  308  the secondary storage device  106  to determine its status. 
         [0036]    If the secondary storage device  106  once again responds  310  with a long busy status, the primary storage device  104  may then notify  312  the host  102  that the primary and secondary volumes  110 ,  114  are in a suspended state. At this point, the host  102  may invoke its recovery procedure. In selected embodiments, this recovery procedure may include freezing  314  all I/O to the volume pairs in the logical subsystem that are in the suspended state. In certain embodiments, the recovery procedure may also include swapping  316  to the secondary storage device  106 , effectively making the secondary storage device  106  the primary storage device  104 . 
         [0037]    The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.