Abstract:
A computer system for managing log information, enabling correct comprehension of system logs for an identical resource before and after migration among plural nodes. A global ID, being unique in the system, is given to a resource (LU) migrated from one file share server to another. The global ID remains the same in the migration destination file share server after migration and log messages for the resource are obtained based on the global ID.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application relates to and claims priority from Japanese Patent Application No. 2005-318721, filed on Nov. 1, 2005, the entire disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a computer system and a method for managing a system log when a resource mapped onto a node is migrated from one node to another.  
         [0003]     Lately, with the dramatic increase in the amount of data managed in information systems, storage network technology has been widely used. In one example of a storage network, plural file share servers (NAS) are connected to a common storage apparatus via a Storage Area Network (SAN). A file share server is also connected to plural host computers via a Local Area Network (LAN). The host computers having heterogeneous operating systems (OS) can share files via file systems in the file share servers.  
         [0004]     A storage apparatus provides storage resources, i.e., logical units to the file systems of the file share servers. When a file share server accesses a logical unit, it creates system log information. UNIX (registered trademark) type OS comes equipped with, as a conventional log management system, syslog daemon, which is regulated by Request for Comments (RFC) and used for obtaining and managing system logs. The syslog daemon is a daemon having functions for supporting programs to create logs. Using the syslog daemon helps to lighten the log management load on various programs.  
         [0005]     A non-patent document, “The BSD Syslog Protocol” (written by C. Lonvick, http://www.fasq.org/rfc/rfc3164.html) describes a means for formatting and centrally-managing log messages, and a means for obtaining logs and specifying storage locations/output locations for the logs based on information types (categories) and severity of the logs. A similar conventional technique for centrally-managing logs from applications distributed on a network is suggested in U.S. Pat. No. 6,470,388 B1.  
       SUMMARY OF THE INVENTION  
       [0006]     When a file share server obtains a system log, resource (logical unit)-identifying IDs set for each log message are set and managed individually and separately by the respective file share servers. Accordingly, when a resource is migrated from one node to another by switching the path to the resource among the file share servers, although the substance of the resource itself is not changed, the ID for identifying the resource changes in the migration destination node (file share server). Accordingly, logs for the resource before migration and logs for the same resource after migration are managed using different IDs. In other words, it is difficult to follow the different IDs for the resource and obtain all their log information.  
         [0007]     Thereupon, it is one aspect of the present invention to provide a computer system for managing log information, whereby system logs for a resource can be accurately followed before and after migration of the resource among nodes. Another aspect of the present invention is to provide a method for managing the log information.  
         [0008]     In order to solve the above problem and to achieve the above objects, the present invention is characterized in that a resource is given an ID that is and remains unique in a system before and after migration.  
         [0009]     Specifically, the first aspect of the present invention provides a computer system having: a plurality of nodes; a resource corresponding to the node; a resource management module for giving a unique ID to the resource and managing the resource while maintaining the unique ID when the resource having the unique ID is migrated from one node to another; and a log management module for associating log information with the unique ID and managing log information for the same resource before and after migration using the unique ID.  
         [0010]     Second aspect of the present invention provides a computer system having: a file share server having file systems shared between host computers; a storage apparatus for providing logical units to the file share server; a path connection module for setting paths between logical units and file systems so that a logical unit can be migrated from one file system to another; a management module for giving a global ID to a logical unit and managing the logical unit while maintaining the global ID when the logical unit is migrated from one file system to another file system; and a log management module for associating log information for a logical unit with a global ID and managing the log information for the same logical unit in a migration source file system and log information for the same logical unit in a migration destination file system using the global ID.  
         [0011]     Third aspect of the present invention provides a method for managing log information including the steps of: mounting a resource on a node; giving a unique ID to the resource and migrating the resource having the unique ID from one node to another; maintaining the unique ID of the resource when migrating the resource; and associating log information with the unique ID and managing the log information for the same resource before and after migration using the unique ID.  
         [0012]     According to the present invention, log information for a resource is associated with a specified ID that does not change before or after migration of the resource from one node to another.  
         [0013]     As explained, according to the present invention, an effect where system logs for an identical resource can be accurately followed before and after migration of the resource among nodes can be achieved. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a system block diagram showing an example of a computer system according to the first embodiment of the present invention.  
         [0015]      FIG. 2  is a block diagram showing an example of LU path setting.  
         [0016]      FIG. 3  is a file system management table.  
         [0017]      FIG. 4  shows a table showing directory entry and inode.  
         [0018]      FIG. 5  is a format for a log message.  
         [0019]      FIG. 6  is an operation flow for a file system program.  
         [0020]      FIG. 7  is an operation flow for a log management program.  
         [0021]      FIG. 8  is a schematic diagram illustrating LU migration.  
         [0022]      FIG. 9  shows a list of log messages.  
         [0023]      FIG. 10  is an operation flow for a log data analysis program.  
         [0024]      FIG. 11  shows a screen showing a log information analysis result.  
         [0025]      FIG. 12  is another operation flow for the log information analysis program.  
         [0026]      FIG. 13  shows a hardware structure where file share servers in  FIG. 1  are incorporated in a high-end storage system. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     An embodiment of the present invention is described below with reference to the attached drawings.  FIG. 1  shows an example of a computer system for managing log information according to an embodiment of the present invention. Each of client computers  2   a ,  2   b , and  2   c  includes a processor  11  (hereinafter called the “CPU”), a network interface control unit  12  (hereinafter called the “network I/F”) connected to a LAN  4 , and memory  13 , all connected to one another via internal communication channels to enable communication. A file access program  101  stored in the memory  13  is a program that is run by the CPU  11  to access the respective file systems managed by the file share servers  1   a  . . .  1   b.    
         [0028]     Each of the file share servers  1   a  and  1   b  has a network I/F  14 , a CPU  15 , memory  16 , and a storage apparatus interface control unit (hereinafter called the “storage apparatus I/F”)  17  for connection with a SAN  5 , all connected to one another via internal communication channels to enable communication.  
         [0029]     Memory  16  stores a file system program  102 , a file share program  103 , and a log management program  104 , that are run by the CPU  15 .  
         [0030]     When the file share program  103  receives a request via the network I/F  14  from the client computer  2   a ,  2   b , or  2   c , it analyzes the type of request and issues a file I/O request to the file system program  102 . The file system program  102  converts the file I/O request to a block I/O request, which is a request for block I/O to a disk in a storage apparatus  6 , and transmits it to the storage apparatus I/F  17 .  
         [0031]     Then, the file system program  102  receives a reply from the storage apparatus I/F  17  and delivers it to the file share program  103 . The file share program  103  transmits the reply via the network I/F  14  to the client computers  2   a ,  2   b  and  2   c , thereby making it possible to share a file among the clients with different OSs.  
         [0032]     The log management program  104  receives log messages created by the file share program  103  and the file system program  102  and transfers them to a management computer  3  via the LAN  4 .  
         [0033]     Incidentally, as instructed by the management computer  3 , the file system program  102  performs LU path setting and file system creation, described later in detail.  
         [0034]     The file share servers  1   a  and  1   b  and the storage apparatus  6  are connected to one another via the SAN  5  to enable communication. The storage apparatus  6  achieves high-speed response by bundling physical disk drives and provides a large number of logical units (hereinafter called the “LU”) to the file share servers  1   a  and  1   b . By setting paths between LUs and the file share servers  1   a  and  1   b , the file share servers  1   a  and  1   b  see the LUs as a single block device and so can access the storage apparatus by block I/O.  
         [0035]     The management computer  3  has a CPU  18 , a network I/F  21  connected to the LAN  4 , an external storage apparatus interface control unit (hereinafter called the “external storage apparatus I/F”)  19  connected to an external storage apparatus  20 , and memory  22 , all connected to one another via internal communication channels to enable communication. The memory  22  stores a log management program  104 , a log analysis program  106 , and a system management program  107 , that are run by the CPU  18 .  
         [0036]     The log management program  104  performs processing to store log messages transferred from the file shared servers  1   a  and  1   b  in the external storage apparatus  20 . The log analysis program  106  is used by an administrator to analyze the log messages stored in the external storage apparatus  20 . The system management program  107  is used by the administrator to instruct the file share servers  1   a  and  1   b  to perform LU path setting, file system creation/mounting, file share setting and migration.  
         [0037]     Processing performed after assignment of LUs in the storage apparatus  6  to the file share servers  1   a  and  1   b  and before file share setting is explained below.  
         [0038]     The administrator instructs the file share servers  1   a  and  1   b  to set paths between the LUs in the storage apparatus  6  and the file share servers, create file systems, mount the file systems, and make file share settings using the system management program  107  in the management computer  3 .  
         [0039]     In each of the file share servers  1   a  and  1   b , the file system program  102  sets, in the storage apparatus  6 , paths between the file share servers and the LUs and gives the LUs LU numbers that are unique in the file share servers  1   a  and  1   b . It also gives the LUs, for which the paths have been set, global IDs that are unique in the system.  
         [0040]     The global IDs are created by adding ID numbers that are unique in the file share servers  1   a  and  1   b  to IP address information for the file share servers  1   a  and  2   b , but they may also be created using MAC addresses instead of the IP addresses. Alternatively, it is also possible to use apparatus IDs that are assigned to the file share servers  1   a  and  1   b  and unique in the system shown in  FIG. 1 .  
         [0041]     Next, the file system program  102  creates file systems using the LUs for which the paths have been set, and gives file system IDs to the file systems, the IDs being unique in the file share servers  1   a  and  1   b . Incidentally, in the present embodiment, one file system is created for one LU.  
         [0042]     As shown in  FIG. 2 , two file systems having the respective file system IDs  1  and  2  are created in the file share server  1   a . An LU having an LU number  1  and a global ID (GDI)  192 . 168 . 1 . 1 . 1  is formed for one file system, and an LU having an LU number  2  and a global ID 192.168.1.1.2 is formed for the other file system.  
         [0043]     Also, in the file share server  1   b , two file systems having file system IDs  1  and  2  are created. An LU having an LU number  1  and a global ID 192.168.1.2.1 is formed for one file system, and an LU having an LU number  2  and a global ID  192 . 168 . 1 . 2 . 2  is formed for the other file system.  
         [0044]     The file system program  102  specifies mount points for the created file systems  21   a  to  21   d  and performs mount processing. A mount point is a point in a directory tree for the connected client computers and the file share servers  1   a  and  1   b . When the file share program finally specifies mount points and makes export settings, file share settings become open to the client computers.  
         [0045]     The information on the given IDs and settings is managed by the file system program using a file system management table shown in  FIG. 3  and the file share program  103  is referred to in response to file access requests from the client computers  2   a ,  2   b  and  2   c . The management table in  FIG. 3  is stored in local memory in the file share servers.  
         [0046]     The file system program  102  also manages, for each file system, directory entry  41  and inode information  44  shown in  FIG. 4  in order to manage files stored in the file systems or directory information.  
         [0047]     The directory entry  41  includes path names  42  for directories or files belonging to file systems and inode numbers  43  assigned to the directories or files.  
         [0048]     An inode specified by an inode number is information indicating an address of a storage area storing the inode information for a file or directory. Inode information for each directory or file includes an access permission  45 , UID information  46  for a user who owns the directory or file, and a disk block address  47 , etc.  
         [0049]     The disk block address  47  is information indicating a storage area in the storage apparatus  6 , in which data of a file or directory specified by the disk block address is actually stored. The flow of processing performed after transmission of a request from the client computer  2   a ,  2   b , or  2   c  to the file share servers  1   a  and  1   b  and before reception of a result as a response is explained below.  
         [0050]     In each of the client computers  2   a ,  2   b , and  2   c , which are host computers, the file access program  101 , which performs mount processing for file systems exported by the file share servers, receives the path name for an access target file or directory and an access request including the content of processing to be executed by the file share servers  1   a  and  1   b  for the file or directory from the user, and transmits the request to the file share servers  1   a  and  1   b.    
         [0051]     Examples of an access request include requests for file creation, directory creation, attribution change, data writing in a file, and data reading from a file, etc. In the present example, explanations are given for the cases where access requests request data writing to a file and data reading from a file.  
         [0052]     The file access program  101  transmits the path name of a file to the file share servers  1   a  and  1   b  and obtains a file handle. It then specifies a file handle value and transmits a request to the file share servers  1   a  and  1   b . A file handle is a value created by the file share program  103  to specify a file or directory.  
         [0053]     A file handle is created using, for example, a file system ID and an inode number. Accordingly, the file share program  103  can obtain a target file system ID and an inode number from the file handle contained in the request from the client computer  2   a ,  2   b  or  2   c . It then makes a request to the file system program by specifying the file system ID and the inode number.  
         [0054]     The file system program  102  specifies an access target&#39;s LU number and block address based on the file ID and the inode number contained in the request and performs reading or writing processing to the storage apparatus I/F  17 .  
         [0055]     The file system program  102  returns the data sent from the storage apparatus via the storage apparatus I/F  17  to the file share program  103 ; Subsequently, the file share program  103  returns the data to the client computer  2   a ,  2   b  or  2   c  via the network I/F  14 .  
         [0056]     The processing above enables the client computers to access, via the LAN, file systems, for which export is set for the client computers, in the same manner as they access local file systems.  
         [0057]     The file share program  103  and the file system program  102  perform processing to obtain log information, which is necessary when recovering from disk failure in the storage apparatus  6 , as well as making changes in the logical structures of disks. Specifically, they create and transmit log messages to the log management program using self-node internal communication.  
         [0058]      FIG. 5  shows a format of a log message. A log message includes: an area  51  where the acquisition time of a request from a client computer is entered; an area  52  where a name of a log-sending client computer is entered; an area  53  where a global ID is entered; and an area  54  where the log message to be set in memory is entered. Incidentally, in the global ID-setting area, the value given to a target LU is set when the log is obtained.  
         [0059]     The log management program  104  is run in the file share servers  1   a  and  1   b  and the management computer  3 ; however, the operation content varies between them. In the file share servers  1   a  and  1   b , the log management program  104  performs processing to transfer received log messages to the management computer  3 , whereas in the management computer  3 , it performs processing to store the received log messages in the local memory  20 . These operations are designated by parameters at start-up.  
         [0060]      FIG. 6  shows an operation flow for the aforementioned file system program  102 . The file system program waits for a file I/O request from the file share program (step  111 ), obtains an access target&#39;s LU number and block address-according to a file ID and an inode number contained in the file I/O request (step  112 ), and makes a block I/O request to the storage apparatus, and receives a result (step  113 ).  
         [0061]     The file system program obtains the global ID of the LU for which the block I/O was conducted (step  114 ), creates a log message and associates the message with the global ID (step  115  and  116 ). It then notifies the file share program of the result (step  117 ) and returns to step  111 .  
         [0062]     An operation flow for the log management program  104  is explained with reference to  FIG. 7 . First, the log management program checks start-up parameters to decide whether or not to transfer a log message to the management computer  3 , and if it decides to transfer the same thereto, it obtains the IP address of the management computer (step  61 ) and waits for a log message (step  62 ).  
         [0063]     When the log management program receives a log message, it checks the start-up parameters to judge whether log transmission has been ordered (step  63 ), performs processing to transfer the log message- to the specified transmission destination (step  64 ), or performs processing to write the log message in the external storage apparatus  20  via the external storage apparatus I/F  19  (step  65 ). Through the processing, the log management program collects log messages from the file share servers  1   a  and  1   b  in the management computer  3  and stores them in memory.  
         [0064]     Migration of an LU among file systems is explained with reference to  FIG. 8 . The management computer  3  checks loads on the CPUs in the file share servers  1   a  and  1   b . If there is a gap between their loads, the management computer  3  migrates an LU in a file system in the file share server with a heavy CPU load to a file system in the file share server with a lighter CPU load so that their. CPU loads are averaged and the response to the client computers can be quickened.  
         [0065]     Migration of an LU is ordered by the management computer  3  to the file system program in the file share servers  1   a  and  1   b . The LU&#39;s file system and a LU path are deleted in a migration source file share server, while in a migration destination file share server, LU path setting, file system creation, mount processing and file share setting are performed.  
         [0066]     A plurality of file systems together form a common name space. Accordingly, as shown in  FIG. 8 , a client computer can access the logical unit  22   c  via the file share server  1   a  with the light CPU load rather than via the file share server  1   b  with the heavy CPU load. Whereas, if the file systems form name spaces in each file share server, the client computers perform remount processing for the file systems.  
         [0067]     As shown in  FIG. 8 , the LU for which the path is switched is identified with the file system ID=2 and LU number=2 in the migration source file server  1   b , however, in the migration destination file share server  1   a , both the file system ID  2  and the LU number  2  are already used, so different numbers are given (in the example of  FIG. 8 , the file system ID changes to 3 and the LU number changes to 3).  
         [0068]     The migration destination file share server obtains a global ID from the management computer  3  and registers it in the file system management table ( FIG. 3 ) when creating the file system.  
         [0069]      FIG. 9  shows a list of log information for the LU for which the path has been switched, the information having been obtained before and after migration. The log information obtained from the migration source file share server and the log information obtained from the migration destination file share server have different LU numbers, however, both pieces of log information have the same global ID, so it can be understood that the log information is about logins or logouts for the same LU.  
         [0070]     In the present example, the number of I/O retries to the LU is output as the log information, therefore, from the log information, it can be understood that I/O retries have been conducted in the migration source file share server.  
         [0071]      FIG. 10  shows an operation flow for the log analysis program  106  in the management computer  3 . The log analysis program  106  waits for an operation instruction from the administrator (step  91 ). When the administrator requests a log search, the log analysis program obtains log search criteria and collects log messages that match the search criteria from the external storage apparatus  20  (steps  92  and  93 ).  
         [0072]     If the administrator does not request collection of relevant logs, the log analysis program displays the collected logs on the screen (steps  94  and  95 ). If the administrator does request collection of relevant logs, it obtains a list of the global IDs set for the collected log messages (step  96 ) and again collects log messages having a global ID matching the LU&#39;s global ID from the external storage apparatus (step  97 ). Then, it merges the log messages collected in steps  93  and  97  and displays them on the screen (step  98 ).  
         [0073]     Following these steps, as shown in  FIG. 11  for example, if the administrator requests log analysis according to only the name of the file share server (server 1 )  1   a  and the LU number (LU 3 ), all log information for the same LU can be searched for.  
         [0074]     Moreover, when the administrator orders filtering and sorting of the log information displayed on the screen according to global ID, the log analysis program redisplays the log messages according to specified filtering and sorting criteria, thereby providing necessary log information to the administrator in an easy-to-read manner (steps  91  and  99 ).  
         [0075]      FIG. 12  shows an operation flow for the log analysis program  106 . Different from the operation flow shown in  FIG. 10 , the operation flow in  FIG. 12  aims to store log data in a local memory disk in a file share server and fetch and transmit requested log data to the management computer as requested by the management computer, The log analysis program  106  in the management computer  3  obtains analysis log information from a user (client computer) (step  121 ). The analysis log information is information for a target related to the to-be-analyzed log information, such as an address of a file share server and an LU number.  
         [0076]     The log analysis program obtains analysis-requested log information from a local storage resource in a target file share server  1   a  (step  122 ). It then obtains the global ID given to the obtained log information (step  123 ), notifies other file share servers  1   b  of the global ID, and obtains log information having a matching global ID (step  124 ). Consequently, all log information for the same LU in the migration source and migration destination file share servers can be extracted. The obtained logs are arranged in a chronological order and displayed on the screen (step  125 ).  
         [0077]      FIG. 13  shows a functional block diagram of a computer system where the file share servers  1   a  and  1   b  in  FIG. 1  are incorporated in a high-end storage system  600 . Components in  FIG. 13  are explained, also mentioning their correspondence relationships with the components in  FIG. 1 .  
         [0078]     A storage system  600  is structured with: a plurality of storage devices  300 ; and a storage device control apparatus  100  for controlling input and output of data to/from the storage devices  300  in response to input/output requests from information processing apparatuses ( 210  to  250 ). The storage devices correspond to the storage apparatus  6  in  FIG. 1 .  
         [0079]     The information processing apparatuses  1  to  3  ( 210  to  230 ) are connected to the storage system  600  via a LAN  400 . They transmit file name-specified data access requests (requests for input/output of data in files, hereinafter called the “file access requests”) to channel control units CHN 1  to CHN 4  ( 110 ) in the storage system  600 . The channel control units will be explained later. The information processing apparatuses  1  to  3  correspond to the aforementioned client computer  2   a  and the management computer  3 .  
         [0080]     A backup device  910  is also connected to the LAN  400 . The backup device  910  communicates with the storage device control apparatus  100  via the LAN  400 , thereby storing backup data of the data stored in the storage devices  300 .  
         [0081]     The storage device control apparatus  100  includes the channel control units CHN 1  to CHN 4  ( 110 ). Via the channel control units CHN 1  to CHN 4  ( 110 ), the storage device control apparatus  100  relays write accesses or read accesses between the information processing apparatuses  1  to  3  as well as the backup device  910  and the storage devices  300 . The channel control units CHN 1  to CHN 4  ( 110 ) individually accept file access requests from the information processing apparatuses  1  to  3 . Specifically, the channel control units CHN 1  to CHN 4 , each assigned a network address (for example, an IP address) on the LAN  400  and corresponding to the file share servers  1   a  in  FIG. 1 , act as NAS to provide NAS services to the information processing apparatuses  1  to  3 .  
         [0082]     Because the channel control units CHN 1  to CHN 4  providing NAS services are included in the single storage system  600 , NAS servers that have conventionally been provided in separate independent computers are integrated in a single storage system  600 . Accordingly, centralized management of the storage system  600  becomes possible and efficiency in maintenance operations, such as various setting and controls as well as failure management and version management, can be promoted.  
         [0083]     Information processing apparatuses  3  and  4  ( 230  and  240 ) are also connected to the storage device control apparatus  100  via a SAN  500 . The SAN  500  is a network for transmitting, between the storage devices  300  and the information processing apparatuses  3  and  4 , data in blocks that are management units in storage areas provided by the storage devices  300 .  
         [0084]     Communication between the information processing apparatuses  3 ,  4  and the storage device control apparatus  100  via the SAN  500  is generally made according to Fibre Channel Protocol. A SAN-compatible backup device  900  is also connected to the SAN  500 .  
         [0085]     The storage device control apparatus  100  also includes channel control units CHF 1  and CHF 2  ( 111 ) in addition to the aforementioned channel control units CHN 1  to CHN 4 . The storage device control apparatus  100  communicates with the information processing apparatuses  3  and  4  and the SAN-compatible backup device  900  via the channel control units CHF 1  and CHF 2  ( 111 ) and the SAN  500 .  
         [0086]     An information processing apparatus  5  ( 250 ) is also connected to the storage device control apparatus  100 , without involving a network such as the LAN  400  or the SAN  500 . Incidentally, another storage system  610 , which is located at a site (secondary site) away from the site (primary site) of the storage system  600 , is connected to the SAN  500 . The storage system  610  is used as a data replication destination apparatus for data replication or remote copy.  
         [0087]     By having the channel control units CHN 1  to CHN 4  ( 110 ), the channel control units CHF 1  and CHF 2  ( 111 ), and the channel control units CHA 1  and CHA 2  ( 112 ) in the storage system  600  in a mixed state, the storage system  600  can be connected to various kinds of networks. In other words, the storage system  600  is a SAN-NAS combined storage system where the storage system  600  is connected to the LAN  400  via the channel control units CHN 1  to CHN 4  and to the SAN  500  via the channel control units CHF 1  and CHF 2 .  
         [0088]     An interconnection network  150  connects the respective channel control units  110  to  112 , shared memory  120 , cache memory  130 , and disk control units  140  to one another. Transmission of commands and data between them is performed via the interconnection network  150 . The interconnection network  150  is configured with a high-speed bus such as an ultrahigh-speed crossbar switch that transmits data by high-speed switching. The interconnection network  150  switches among paths between NAS file systems and the logical units provided by the storage devices  300 .  
         [0089]     The shared memory  120  and the cache memory  130  are memory apparatuses shared by the channel control units  110  to  112  and the disk control units  140 . The shared memory  120  is mainly used for storing control information and commands while the cache memory  130  is mainly used for storing data. The disk control units  140  always monitor the shared memory  120  and when they determine that a write command has been written in the shared memory  120 , the relevant disk control unit  140  reads write data from the cache memory  130  and writes it in the storage devices  0 . 300  according to the write command.  
         [0090]     Meanwhile, if the data input/output command a channel control unit ( 110 ,  111  or  112 ) receives from an information processing apparatus ( 210 ,  220 ,  230 ,  240  or  250 ), is a read command, the channel control unit writes the read command in the shared memory  120  and checks whether the read target data exists in the cache memory  130 .  
         [0091]     The disk control units  140  convert logical address-specified data access requests transmitted from the channel control units  110  to  112  to the storage devices  300  to physical address-specified data access requests, and write or read data in or from the storage devices  300  in response to I/O requests output from the channel control units  110 .  
         [0092]     The storage devices  300  are equipped with one or more disk drives (physical volumes) and provide storage areas that can be accessed from the information processing apparatuses ( 210  to  250 ). Logical units, where storage spaces of one or more physical volumes are combined, are set for the storage areas provided by the storage devices  300 . The logical units set for the storage devices  300  include user logical units that can be accessed from the information processing apparatuses ( 210  to  250 ) and system logical units used for controlling the channel control units  110  to  112 .  
         [0093]     The logical units allocated to the physical volumes provided by the storage devices  300  can be accessed from the channel control units  110 . The channel control units  110  may share the same logical unit. A management computer may be incorporated in the storage system. A management computer  160  is for maintaining and managing the storage system  600  and is connected to the respective channel control units  110  and the disk control units  140  via an internal LAN  151 . By operating the management computer  160 , an operator can set disk drives in the storage devices  300 , set logical units, and install micro programs that are run by the channel control units  110  to  112  and the disk control units  140 .  
         [0094]     Incidentally, as already described in the explanation for the embodiment, a log management module is realized by the log management program in the file share server  1   a  and  1   b  and the log analysis program  106  and the log management program  104  in the management computer  3 . A resource management module is realized by the file share program  102  and the file system program  103  in the file share servers  1   a  and  1   b  and the system management program  107  in the management computer  3 . A path control program is realized by the file system program  102  in the file share server  1   a  and  1   b  and the system management program  107  in the management computer  3 . The embodiment explained so far is merely an example and may be changed as appropriate as long as it does not deviate from the gist of the present invention.