Abstract:
A disk-array apparatus comprises a plurality of disk-medium modules, a first through a fourth memory modules, and a director module connected to a host. The first and the third memory modules are combined with each other so as to serve as a first memory module-pair. The second and the fourth memory modules are combined with each other so as to serve as a second memory module-pair. The director module writes, when a future occurs in the first memory module, fast-write data to the second and the fourth memory modules of the second memory module-pair and appoint two memory modules optionally selected from the second through the fourth memory modules for respectively performing cache control regions.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a disk-array apparatus for use in combination with a host which serves as an upper-layer data processing apparatus such as a computer apparatus and which can write/read data to/from said disk-array apparatus and having a plurality of disk-medium modules and, in particular, to the disk-array apparatus further having a disk cache interposed between the host and the disk-medium modules for temporarily memorizing the data. 
     Generally, the disk-array apparatus has the disk cache (cache memory) in order to accelerate an access speed by the host to the disk-array apparatus. When the host performs a writing process (step) for writing data to the disk-array apparatus, writing data to be written into the disk-array apparatus are temporarily memorized in the disk cache. When the writing data is temporarily memorized in the disk cache, the disk cache or the disk-array apparatus performs a fast-write process. The fast-write process serves to inform to the host that the writing process is completed. 
     In the fast-write process, when the writing data transmitted from the host is memorized in the disk cache (a memory module), the above-mentioned information expressing that the writing process is completed is informed to the host. Therefore, the writing data to be updated may be disappeared or vanished by unexpected error before the writing data is practically written in the disk-array apparatus. This is called a data loss. In order to avoid the data lops, it is necessary to make the writing data into duplex data by providing backing-up data. Namely, the disk-array apparatus generally duplicates the writing data to make the duplex data by providing dual memory modules in order to avoid the data loss. 
     By making the writing data into duplex data as mentioned above, the disk-array apparatus will have redundancy. 
     However, if one of the memory modules of the disk-array apparatus fails, the memory modules perform degraded or degenerate mode by the other one of the memory modules. In case where the memory modules are operated in the degraded mode, the redundancy is spoiled. If the other one of the memory modules fails when the disk-array apparatus spoiling the redundancy performs the fast-write process, the writing data may be damaged. 
     On the other hand, if the fast-write process is forbidden, without exception, during the memory modules perform in the degraded mode, the writing data will not be damaged although the other one of the memory modules fails. However, the writing process will not be increased in transmission speed. Namely, the disk-array apparatus undesirably and considerably reduced in its performance. 
     The above-mentioned points are both very important for the disk-array apparatus to perform the writing process in high transmission speed and to avoid the data lose. Therefore, they are preferable and necessary for the disk-array apparatus to perform the writing process in high transmission speed and to avoid the data loss at the same time. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to deal with disadvantages mentioned above and to therefore provide a disk-array apparatus to be used for a host capable of performing a writing process in high transmission speed and to surely avoiding a data loss at the same time. 
     The other object, features, and advantages of this invention will become clear as the description proceeds. 
     This invention is directed to a disk-array apparatus for use in combination with a host which serves as a data processing apparatus, the disk array apparatus comprising a plurality of disk-medium modules, a plurality of memory modules, and a director module connected to the hose, the disk-medium modules, and the memory modules, the director module being for carrying out writing and reading operations of writing and reading the data to and from the disk-medium modules under control of the host and for temporarily storing the data to the memory modules when the director module carries out the writing and the reading operations. The memory modules comprise a first through a fourth memory modules. The first and the second memory modules are combined with each other so as to serve as a first memory module-pair. The third and the fourth memory modules are combined with each other so as to serve as a second memory module-pair. The director module writes, when a failure occurs in the fist memory module, fast-write data to the second and the fourth memory modules of the second memory module-pair and appoint two memory modules optionally selected from the second through the fourth memory modules for respectively performing cache control regions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a disk-array apparatus according to an embodiment of this invention; 
     FIG. 2 is a block diagram, showing control and data regions of memory modules of the disk-array apparatus shown in FIG. 1 when the disk-apparatus is operated in a normal state, for illustrating in detail operation of the disk-array apparatus; 
     FIG. 3 is a block diagram, showing the control and the data regions of the memory modules of the disk-array apparatus shown in FIG. 1 when one of the memory modules fails, for illustrating in detail operation of the disk-array apparatus; and 
     FIG. 4 is a block diagram, showing the control and the data regions of the memory modules of the disk-array apparatus shown In FIG. 3 when another of the memory modules further fails, for illustrating in detail operation of the disk-array apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, a preferred embodiment of this invention will be described with reference to Drawings. 
     Referring to FIG. 1, a disk-array apparatus according to the embodiment of this invention is used in combination with a host  100  through a host interface  17 . The host  100  solves as a data processing apparatus and can write/read data to/from the disk-array apparatus. 
     The disk-array apparatus comprises a plurality of disk-medium modules  16  and director modules  15  for controlling the disk-medium modules  16  and a plurality of memory modules mentioned below based on writing and reading operation by the host  100 . The disk-medium modules  16  are used for writing/reading data thereto/therefrom by the host  100 . The director modules  15  control the disk-medium modules  16  and the memory modules based on writing and reading operation by the host  100 . 
     The disk-array apparatus further comprises a first through a fourth memory modules  11  through  14 . The first to the fourth memory modules  11  to  14  serve as the memory modules interposed between the disk-medium modules  16  and the host  100  through the director modules  15 . The first to the fourth memory modules  11  to  14  can temporarily memorize data as the disk caches. 
     When the disk-array apparatus is received an I/O (Input and Output) command through the host interface  17  from the host  100 , the director modules  15  analyzes the I/O (Input and Output) command. Consequently, the director modules  15  perform an I/O operation based on the I/O command analyzed. For example, if the I/O command is for ordering the disk-array apparatus to Input the writing data, the director modules  15  transmit the writing data from the host  100  through the first to the fourth memory modules  11  to  14  to the disk-medium modules  16 . On the other hand, if the I/O command is for ordering the disk-array apparatus to output the reading data, the director modules  15  transmit the reading data from the disk-medium modules  16  through the first to the fourth memory modules  11  to  14  to the host  100 . 
     Next, arrangement of the data in the first to the fourth memory modules  11  to  14  during the disk-array apparatus performs the degraded or the degenerate mode will be described, referring to FIGS. 1 and 2. 
     As shown in FIG. 2, the first memory module  11  is appointed to perform a main control region  21  and a main data region  22 . The second memory module  12  is appointed to perform a sub control region  23  and a sub data region  24 . The third memory module  13  is appointed to perform a reserve control region  25  and a main data region  26 . The fourth memory module  14  is appointed to perform a reserve control region  27  and a sub data region  28 . 
     A control data for entirely controlling the first to the fourth memory modules  11  to  14  is memorized in the main control region  21  of the first memory module  11 . Furthermore,the same data as the control data is memorized in the sub control region  23  of the second memory module  12 . Both of the main data regions  22  and  26  of the first and the third memory modules  11  and  13  are used as the disk caches. Consequently, in the main data regions  22  and  26 , the reading data from the disk-medium modules  16  or the writing data from the host  100  is memorized. The same data as the data memorized in the main data regions  22  and  26  are memorized as the other of the duplex data in the sub data regions  24  and  28 , respectively. The main data, the sub data, the main data, and the sub data regions  22 ,  24 ,  26 , and  28  can be used as both of reading cache and writing cache. 
     If the first memory module  11  fails and therefore the reading and/or the writing data memorized in the main control and the main data regions  21  and  22  are lost, the reading and/or the writing data are never lost. This is because the disk-array apparatus makes the reading and/or the writing data into the duplex data as mentioned below. 
     Referring to FIGS. 1 to  3 , when the first memory module  11  fails, the reading and/or the writing data memorized in the main control and the main data regions  21  and  22  (shown in FIG. 2) are lost. Namely, the main data regions  21  and  22  are appointed as impossible regions  31  and  32  as shown in FIG. 3 by the director modules  15 . When the impossible regions  31  and  32  are formed, the director modules  15  respectively change the sub control region  23  of the second memory module  12  (shown in FIG. 2) into the warn control region  33  as shown in FIG.  3 . 
     The director modules  15  further change the reserve control region  25  of the third memory module  13  (shown in FIG. 2) into a sub control region  35  as shown in FIG.  3 . 
     Furthermore, the director modules  15  change the sub data region  24  of the second memory module  12  (shown in FIG. 2) into main data region  34  as shown in FIG.  3 . 
     Herein, no sub data region corresponding to the main data region  34  exists. In addition, although the main data and the sub data regions  26  and  28  of the third and the fourth memory modules  13  and  14  (shown in FIG. 2) are respectively changed into main data and sub data regions  36  and  38  of the third and the fourth memory modules  13  and  14  as shown in FIG. 3, these regions are only changed ostensibly but not changed substantially. Furthermore, the reserve control region  27  (shown in FIG. 2) of the fourth memory module  14  is also changed ostensibly into a reserve control region  37  as shown in FIG.  3 . 
     Thus, the main data region  34  is used as the reading cache only. On the other hand, the main data and the sub data regions  36  and  38  are used as the writing caches. 
     Afterward, during the disk-array apparatus performs the degraded or the degenerate mode, the first memory module  11  failing is repaired or changed into the new memory module so that the disk-array apparatus is restored in redundancy. 
     However, another memory module except the first memory module  11  further may fail before the repair or the change of the first memory module  11 . For example, if the second memory module  12  fails, the data memorized in the main data region  34  shown in FIG. 3 are lost. However, because the data memorized in the main data  34  is only used as the reading cache, the disk-array apparatus perform normal operation. 
     Referring to FIGS. 1,  3 , and  4 , when the second memory module  12  also fails in addition to the first memory module  11  as mentioned above, the main control and the main data regions  33  and  34  (shown in FIG. 3) of the second memory module  12  are appointed as impossible regions  43  and  44  as shown in FIG. 4 by the director modules  15 . In addition, the impossible regions  31  and  32  (shown in FIG. 3) of the first memory module  11  is changed ostensibly into the impossible regions  41  and  42  as shown in FIG.  4 . 
     Furthermore, the sub control region  35  (shown in FIG. 3) of the third memory module  13  is also changed into a main control region  45  as shown in FIG. 4 by the director modules  15 . In addition, the main data, the reserve control, and the sub data regions  36 ,  37 , and  38  (shown in FIG. 3) are changed ostensibly into main data, reserve control, and sub data regions  46 ,  47 , and  48  as shown in FIG.  4 . 
     During the memory modules  11  and  12  fail as mentioned above and shown in FIG. 4, the director modules  15  inhibit the host  100  from writing/reading data to all of the first to the fourth memory modules  11  to  14 . In other word, the director modules  15  inhibit I/O (inputting and Outputting) operation between the host  100  and the all of the first to the fourth memory modules  11  to  14 . When the director modules  15  inhibit the I/O operation, the director modules  15  transmit in a short time all of the fast-write data memorized in the third and the fourth memory modules  13  and  14  as the caches to the disk-medium modules  16 . Thus, the fast-write data are assured but never lost. Afterward, the first and the second memory modules  11  and  12  failing are repaired or changed into the new memory modules so that the disk-array apparatus is restored in redundancy and can perform the normal mode. 
     While this invention has thus far been described in conjunction with the embodiment thereof, it will readily be possible for those skilled in the art to put this invention into practice in various other manners.