Abstract:
Systems and methods directed to preventing a single point of failure by utilizing N_Port ID Virtualization (NPIV). During some procedures used by storage subsystems, such as migration, there is oftentimes only a single path from a host to a storage subsystem, which causes a potential single point of failure for the entire system. By utilizing NPIV, this problem may be mitigated.

Description:
[0001]    BACKGROUND 
         [0002]    1. Field of the Invention 
         [0003]    The present application is generally directed to storage systems having one or more storage subsystems or storage units, and more specifically, to preventing the creation of single points of failure in storage systems. 
         [0004]    2. Description of the Related Art 
         [0005]    In order to maintain the consistency of the data in a storage system, where an existing storage subsystem is to be replaced by a replacement storage subsystem due to failure, obsolescence or a need for maintenance, conventional storage subsystems typically require that all of the I/O to the replaced storage unit be halted. Recently, it has been possible to replace an existing storage subsystem with a replacement storage subsystem without stopping the host I/O, by using N_Port ID Virtualization (NPIV) technology. The path for the I/O connections between a host and a storage subsystem is provided through ports, each having a name or identifier. 
         [0006]    NPIV allows for the creation of one or more virtual ports on one physical port. By this port virtualization, NPIV also allows port migrations accompanied by the device, such as host computers, storage system, to change access paths. As explained in U.S. Publication 2010/0070722, by using the multiple port environment, users can migrate data between two storage subsystems without disruption. 
         [0007]    However, there are several unresolved issues with regard to the solution proposed by the foregoing publication. For example, for a storage system that utilizes Fiber Channel (FC), suspension of all I/O is required for several seconds in order to logout and re-login. During such a process, the path configuration of the storage subsystem reduces to a single path, which creates a single point of failure should the path be disrupted. 
         [0008]    Therefore, there is a need to prevent such a single point of failure. 
       SUMMARY OF THE INVENTION 
       [0009]    The invention is directed to methods and systems that substantially obviate one or more of the above and other problems associated with conventional techniques for storage systems, particularly the replacement of storage subsystems and prevention of possible single points of failure within those storage subsystems. 
         [0010]    Aspects of the present invention may include a system with a host including a plurality of physical ports; a source storage system; a target storage system; and a first switch. The host accesses the source storage system via the first switch. In response to a migration request to migrate data from the source storage system to the target storage system, a first path and a second path are added between the host and the target storage system via the first switch, wherein the addition of the first path and the second path is conducted before terminating a path between the host and the source storage system. 
         [0011]    Aspects of the present invention include a system which may include a host including a plurality of physical ports; a source storage system; a first switch and a target storage system. The host may access the source storage system via the first switch; and in response to a migration request to migrate data from the source storage system to the target storage system, the source storage system may create a virtual port to establish a first path between the host and the target storage system via the first switch; wherein the virtual port is created by N_Port ID Virtualization (NPIV). 
         [0012]    Aspects of the present invention include a method of migrating data from a source storage system to a target storage system. The method may involve receiving a migration request from a server to migrate data from said source storage system to said target storage system; creating a first path and a second path between a host to the target storage system in response to the migration request, wherein the creating the first path and the second path is conducted before terminating a path between a host and the source storage system; and, wherein a first virtual port is created to said target storage system for creating the first path and wherein N_Port ID Virtualization (NPIV) is used to create the first virtual port. 
         [0013]    Additional aspects related to the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Aspects of the invention may be realized and attained by means of the elements and combinations of various elements and aspects particularly pointed out in the following detailed description and the appended claims. 
         [0014]    It is to be understood that both the foregoing and the following descriptions are exemplary and explanatory only and are not intended to limit the claimed invention or application thereof in any manner whatsoever. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The accompanying drawings, which are incorporated in and constitute a part of this specification exemplify the embodiments of the present invention and, together with the description, serve to explain and illustrate principles of the inventive technique. Specifically: 
           [0016]      FIG. 1  illustrates one physical and logical configuration of a system according to embodiments of the invention. 
           [0017]      FIG. 2  illustrates an exemplary table and flowchart of aspects of the system according to an embodiment of the invention. 
           [0018]      FIG. 3  illustrates exemplary tables of aspects of the system according to an embodiment of the invention. 
           [0019]      FIG. 4  illustrates an exemplary volume management table according to an embodiment of the invention. 
           [0020]      FIG. 5  illustrates an exemplary external volume management table and flowchart according to an embodiment of the invention. 
           [0021]      FIG. 6  illustrates an exemplary data migration table and flowchart according to an embodiment of the invention. 
           [0022]      FIG. 7  illustrates an exemplary storage migration management flowchart according to an embodiment of the invention. 
           [0023]      FIG. 8  illustrates an exemplary recovery control flowchart. 
           [0024]      FIG. 9  illustrates an example of migration procedures according to an embodiment of the invention. 
           [0025]      FIG. 10  illustrates an exemplary procedure for introducing the migration target storage according to an embodiment of the invention. 
           [0026]      FIG. 11  illustrates exemplary procedures related to the flowchart of  FIG. 7  according to an embodiment of the invention. 
           [0027]      FIG. 12  illustrates additional example of procedures related the flowchart of  FIG. 7  according to alternative embodiments of the invention. 
           [0028]      FIG. 13  illustrates additional exemplary procedures related to the flowchart of  FIG. 7  according to embodiments of the invention. 
           [0029]      FIG. 14  illustrates additional exemplary procedures related to the flowchart of  FIG. 7  according to embodiments of the invention. 
           [0030]      FIG. 15  illustrates additional exemplary procedures related to the flowchart of  FIG. 7  according to embodiments of the invention. 
           [0031]      FIG. 16  illustrates additional exemplary procedures related to the flowchart of  FIG. 7  according to embodiments of the invention. 
           [0032]      FIG. 17  further illustrates an exemplary sequence based on  FIGS. 9 to 16 , according to embodiments of the invention. 
           [0033]      FIG. 18  illustrates another possible physical and logical configuration of a system according to embodiments of the invention. 
           [0034]      FIG. 19  illustrates another exemplary table and flowchart of aspects of the system according to embodiments of the invention. 
           [0035]      FIG. 20  illustrates additional example migration procedures according to embodiments of the invention. 
           [0036]      FIG. 21  illustrates an exemplary flowchart for Storage Migration Management  511 . 
           [0037]      FIG. 22  further illustrates an exemplary procedure during Step  511 - 2  to Step  511 - 11  according to an embodiment of the invention. 
           [0038]      FIG. 23  further illustrates an exemplary procedure related to Step  511 - 13  and Step  511 - 17  according to an embodiment of the invention. 
           [0039]      FIG. 24  further illustrates an exemplary procedure related to Step  511 - 13  and Step  511 - 17  according to an embodiment of the invention. 
       
    
    
       [0040]      FIGS. 1 ,  9 - 16 ,  18  and  22 - 24  utilize differing lines to illustrate the flow of procedure, the flow of I/O and the physical path for various embodiments of the invention, as shown in the legend. Specifically, the solid lines with arrowheads indicate the flow of procedure, the dashed lines indicate the flow of I/O, and the solid bolded lines without any arrowheads indicate the physical path, respectively. 
       DETAILED DESCRIPTION 
       [0041]    In the following detailed description, reference will be made to the accompanying drawings, in which identical functional elements are designated with like numerals. The aforementioned accompanying drawings show by way of illustration, and not by way of limitation, specific embodiments and implementations consistent with principles of the present invention. These implementations are described in sufficient detail to enable those skilled in the art to practice the invention and it is to be understood that other implementations may be utilized and that structural changes and/or substitutions of various elements may be made without departing from the scope and spirit of present invention. The following detailed description is, therefore, not to be construed in a limited sense. Additionally, the various embodiments of the invention as described may be implemented in the form of a software running on a general purpose computer, in the form of a specialized hardware, or combination of software and hardware. 
         [0042]    According to the embodiments of the invention, in order to prevent a single-point-of-failure in a storage system, a storage subsystem and a host computer temporally makes another path on the physical path (first path) by using NPIV. The process requires a change in the name of ports along an existing first I/O path. According to the embodiments of the invention, each port&#39;s name is a virtual port name. The name of a port along the first I/O path to the storage subsystem that is to be replaced is changed. Based on that changed port name, the storage subsystem migrates the data and the first path to a new or replacement storage subsystem. Subsequently, the old storage subsystem and the host computer removes the second path. In this manner, it is thereby possible to keep an I/O path between the old storage subsystem and host computer after the migration is completed. 
       First Embodiment 
       [0043]    In a system where the host connects to the migration source storage via one or more switches, a temporal path is added utilizing NPIV to connect the host to the migration source storage via the first switch. During the migration, when the paths connecting the host to the migration source storage are removed and connections are established at the target source storage, the temporal path maintains a redundant connection between the host and the migration source storage to ensure that there is always at least two paths between the host and the migration source storage until the migration process is completed. After the migration process is completed, the temporal path is then removed. 
         [0044]      FIG. 1  illustrates an example of a physical and logical configuration of the system according to an embodiment of the invention. 
         [0045]    Operator  1 : The operator may set and change configuration of host computer, switch devices and storage devices. 
         [0046]    Host Computer  100 : The host computer may include one or more Host Bus Adapters (HBA)  101 , to interface to the storage. The HBA may have a port with NPIV functionality which connect to port  201  in Switch  200 . Normally the Host Computer  100  has two or more HBAs  101  for redundancy, which are shown as  101   a ,  101   b  in the Figure. 
         [0047]    Application  110 : The Application  110  generates read and write I/Os. Data for the Application  110  is stored in the Migration Source Storage Subsystem  300  or the Migration Target Storage Subsystem  400 . 
         [0048]    Multi Path Management  111 : The Multi Path Management  111  manages paths. For example, the Multi Path Management can create a multi path configuration for path redundancy and path performance. If a path failure occurs, the Multi Path Management blocks the failure path and transfers I/Os to an other active path. 
         [0049]    OS  112 : The OS  112  manages drives (e.g. HBA Driver  113 ), the physical configuration of the Host computers (HBA  101 ) and the schedules and the resources of other jobs (e.g. Application  110  and Multi Path Management  111 ). 
         [0050]    HBA Drivers  113 : The HBA Driver  113  controls a physical or a virtual port. The Host computer  100  can have a plurality of HBA Drivers  113 , which are shown as HBA Driver  113   a,    113   b,    113   c.    
         [0051]    Switches  200 : The Switch  200  connects the Migration Source Storage Subsystem  300 , the Migration Target Storage Subsystem  400  and the Host Computer  100 . There are two or more Switches  200  for path redundancy, as shown, with respect to switch  200   a  and  200   b.  These switches support NPIV functionality. 
         [0052]    Ports  201 : The Ports  201  connects cables between HBAs  101 , Ports  301  and/or Ports  401 . 
         [0053]    Migration Source Storage Subsystem  300 : The Migration Source Storage Subsystem  300  is the storage subsystem that is to be removed after data migration to Migration Target Storage Subsystem  400 . 
         [0054]    Ports  301 : The Ports  301  connect to Port  201  in Switch  200 . The Migration Source Storage Subsystem  300  has two or more Ports for redundancy, as shown with respect to Ports  301   a  and  301   b.  Each of Ports  301  has NPIV functionality and is a target port. 
         [0055]    LUs  320 : At least one logical unit—LU  320 —is allocated to one port. One port can have a plurality of LUs. In this example, there are a plurality of LUs  320 , as shown in  FIG. 1  with respect to LU  320   a  and  320   b.  LU  320   a  and LU  320   b  share one Logical Volume  321  for redundancy. 
         [0056]    Logical Volume  321 : The Logical Volume  321  stores data and typically comprises disk drives to make RAID groups. 
         [0057]    Port Management  311 : The Port Management manages the port configuration, port name, and path status of each port. 
         [0058]    Volume Management  312 : The Volume Management  312  manages the relationship between Ports  301 , LUs  320  and Logical Volume  321 . 
         [0059]    Migration Target Storage Subsystem  400 : The Migration Target Storage Subsystem  400  is operative to replace Migration Source Storage Subsystem  300 . 
         [0060]    Ports  401 : Same as Ports  301   
         [0061]    Ports  402 : Same as Ports  301  except they are initiator ports. 
         [0062]    Port Management  411 : Same as Port Management  311  except the management is applied to Ports  401   a,    402   b,    401   a  and  401   b  instead of Ports  301   a  and  302   b.    
         [0063]    Volume Management  412 : Same as Volume Management  312  except initially there are no LUs or logical volumes because in this case the Migration Target Storage Subsystem  400  is a new storage subsystem storing no data at first. 
         [0064]    External Volume Management  413 : The External Volume management conducts I/O transfer management and control to other storage. 
         [0065]    Data Migration  414 : The Data Migration conducts data transfer and configuration management and control migration from the other storage subsystem. 
         [0066]    Storage Management Server  500 : The Storage Management Server  500  manages the configuration of the Migration Source Storage Subsystem  300  and the Migration Target Storage Subsystem  400 , and the migration between these storage subsystems. This server can be made redundant to prevent failure. 
         [0067]    Storage Migration Management  511 : The Storage Migration Management  511  manages the data/configuration migration process between the Source Storage Subsystem  300  and the Migration Target Storage Subsystem  400 . 
         [0068]    Recovery Control  512 : Recovery Control  512  manages the migration process and recovers the configuration if path failure occurs. 
         [0069]      FIG. 2  illustrates an exemplary table and flowchart of the Multi Path Management unit  111 . 
         [0070]    Multi Path Management table  111 - 1 : The Multi Path Management Table manages a relationship between the device file, port and LU. 
         [0071]    Device Name  111 - 1 : A device filename which is provided to user and applications. 
         [0072]    Port Number  111 - 1 - 2 : Indicates the Port number to which a LU is connected. One device file can utilize a plurality of LUs. Each LU is allocated on a different path. 
         [0073]    LU Number  111 - 1 - 3 : An ID of the LU in the path. 
         [0074]    Path Status  111 - 1 - 4 : Manages the status of a path that the port establishes. “Active” indicates that the path can be used. After a path failure occurs, the status of the path/port changes to “Fault”. “Fault” indicates that the path cannot be used because of failure. After the failure is recovered the status changes to “Logging-in”. “Logging-in” indicates that the path cannot be used temporally because the path is not established yet. After the path is established (storage port logs in), the status is changed to “Active”. 
         [0075]    Multi Path Management Program  111 - 2 : This program selects an active path to transfer I/O. 
         [0076]    Step  111 - 2 - 2 : The Host  100  selects one active path from the Multi Path Management table  331 - 1  for an accessed device file. One exemplary algorithm for the selection is “Round-robin Scheduling”, as is known in the art. 
         [0077]    Step  111 - 2 - 3 : The Host  100  transfers I/O to HBA Driver  101 , which relates to selected ports. If the I/O has failed, then there is a change of the status in Path Status  111 - 1 - 4  to “Fault”. 
         [0078]      FIG. 3  illustrates exemplary tables for Port Management  311 . 
         [0079]    Port Name Management Table  311 - 1 : The Port Name Management Table manages the port names of each port. 
         [0080]    Port Number  311 - 1 - 1 : An ID for the port. 
         [0081]    Port Attribution  311 - 1 - 2 : Indicates the purpose of the port. “Target” indicates that the port is used for target port. “Initiator” indicates that the port is used for initiator port. 
         [0082]    Name List  311 - 1 - 3 : A name list of a port. One port can have a plurality of names. These names are unique within the system. 
         [0083]    Path Management Table  311 - 2 : The Path Management Table manages the path status of each (physical and virtual) port. 
         [0084]    Port Name  311 - 2 - 1 : Indicates the name of the port. The names are listed in Name List  311 - 1 - 3   
         [0085]    Path Status  311 - 2 - 2 : Indicates the status of the path. “Active” indicates that the path can be used. After a path failure occurs, the status of the path/port changes to “Fault”. “Fault” indicates that the path cannot be used because of failure. After the failure is recovered the status changes to “Logging-in”. “Logging-in” indicates that the path cannot be used temporally because the path is not established yet. After the path is established (host port logs in), the status is changes to “Active”. 
         [0086]      FIG. 4  illustrates an exemplary table for Volume Management  312 . 
         [0087]    Volume Management Table  312 - 1  may include: 
         [0088]    Logical Volume Number  312 - 1 - 1 : An ID for a logical volume. 
         [0089]    Port Name  312 - 1 - 2 : The port name of the LU using the logical volume. 
         [0090]    LU Number  312 - 1 - 3 : The LU number of the LU using the logical volume. The number is unique in the path (same port name). 
         [0091]      FIG. 5  illustrates an example table and flowchart for External Volume Management  413 . 
         [0092]    External Volume Management Table  413 - 1  may include: 
         [0093]    Target Port/LU Name  413 - 1 - 1 : Indicates the target port and the name of the LU where external volume functions are being applied. 
         [0094]    Initiator Port Number  413 - 1 - 2 : An Initiator port name from which the LU transfers I/O. 
         [0095]    External Port/LU Name  413 - 1 - 3 : The target port and LU name of an external volume. 
         [0096]    External Volume Management  413  may include an External Volume Management Program  413 - 2 . The flow of the Management Program may include: 
         [0097]    Step  413 - 2 - 2 : When the program receives I/O, the Migration Target Storage Subsystem  400  finds the accessed LU with the Target Port/LU Name  413 - 1 - 1 , selects an external volume, and transfers I/O to the external volume. 
         [0098]      FIG. 6  illustrates an example table and flowchart for Data Migration  414 . 
         [0099]    Data Migration Table  414 - 1  may include: 
         [0100]    Logical Volume Number  414 - 1 - 1 : The ID of a logical volume where data is stored after the migration. 
         [0101]    Migration Source Volume Number  414 - 1 - 2 : The ID of the LU where data is migrated from. It can store a plurality of volume names if the path has redundancy. 
         [0102]    The Data Migration may include a Data Migration Program  414 - 1 - 2  as shown in  FIG. 6 . 
         [0103]    Step  414 - 2 - 2 : the Migration Target Storage Subsystem  400  reads data from the migration source volume as described in Data Migration Table  414 - 1  and stores the data to designated logical volume. 
         [0104]    Step  414 - 2 - 3 : After the data copy is finished, the Migration Target Storage Subsystem  400  deletes the LU name in the External Volume Management Table  413 - 1  and stores the relationship between the LUs and the logical volume into the Volume Management Table  412 - 1 . 
         [0105]      FIG. 7  illustrates an exemplary flowchart for Storage Migration Management  511 . 
         [0106]    Step  511 - 2 : The storage management server gathers the configuration information from the Migration Source Storage Subsystem  300 . 
         [0107]    Step  511 - 3 : The Storage Management Server  500  sends the path information to Port Management  411  to establish a path from Ports  402   a  and  402   b  to Ports  301   a  and  301   b.    
         [0108]    Step  511 - 4  and Step  511 - 5 : The Storage Management Server  500  waits for the path to be established. If the path isn&#39;t established, the Storage Management Server  500  notifies the user to check the condition of the cables or the security setting. 
         [0109]    Step  511 - 6 : The Storage Management Server  500  orders the Port Management  311  to set new virtual target ports on Port  301   a  and  301   b.    
         [0110]    Step  511 - 7 : The Storage Management Server  500  orders the new virtual target ports on Port  301   a  and  301   b  to log in the fabric. 
         [0111]    Step  511 - 8 : The Storage Management Server  500  orders the Volume Management  312  to provision new LUs  320   c  and  320   d,  using the new virtual target ports on Ports  301   a  and  301   b,  and sharing the same Logical Volume  321  of LU  320   a  and  320   b.    
         [0112]    Step  511 - 9 : The Storage Management Server  500  informs the Operator  1  to make new connections from the Host Computer  100  to the new virtual target ports on Port  301   a  and  301   b.    
         [0113]    Step  511 - 10  and Step  511 - 11 : The Storage Management Server  500  waits for the completion of the path establishing from Ports  101   a  and  101   b  to the new virtual target ports on  301   a  and  301   b.  During these steps, the Operator  1  sets new virtual initiator ports on Port  101   a  and  101   b,  runs HBA Drivers  113   c  and  113   d  for the new virtual initiator ports, and registers the virtual initiator port to Multi Path Management  111 . 
         [0114]    Step  511 - 12 : The Storage Management Server  500  orders the Port Management  311  to log out the existing (not the virtual) target ports on Port  301   a  and  301   b.  Additionally, the storage management server may order the Port Management  311  to delete the name of the existing (not the virtual) target ports on Port  301   a  and  301   b.    
         [0115]    Step  511 - 13 : The Storage Management Server  500  orders the Port Management  411  to name the deleted name as virtual target ports to Port  401   a  and  401   b.    
         [0116]    Step  511 - 14 : The Storage Management Server  500  orders the Extended Volume Control  413  to make new LUs as external volumes mounting LU  320   c  and  320   d.    
         [0117]    Step  511 - 15 : The Storage Management Server  500  orders the Port Management  411  to log in the virtual target ports on Port  401   a  and  401   b.    
         [0118]    Step  511 - 16  and Step  511 - 17 : The Storage Management Server  500  waits for the establishment of the path. During Step  511 - 12  and Step  511 - 14 , the path between Ports  101   a / 101   b  and  301   a / 301   b  is active because of the path between the respective virtual ports. 
         [0119]    Step  511 - 18 : The Storage Management Server  500  informs the Operator  1  to terminate the virtual initiator ports on Port  101   a  and  101   b.    
         [0120]    Step  511 - 19  and Step  511 - 20 : The Storage Management Server  500  waits for the completion of the logging-out of the virtual initiator ports on Port  101   a  and  101   b.    
         [0121]    Step  511 - 21 : The Storage Management Server  500  orders the Data Migration  414  to migrate data and configuration from Logical Volume  321  to  421 . 
         [0122]    Step  511 - 22 : After the migration is finished, the Storage Management Server  500  deletes virtual target ports on Port  301   a  and  301   b.    
         [0123]    Step  511 - 23 : The Storage Management Server  500  informs the user to remove Migration Source Storage Subsystem  300 . 
         [0124]      FIG. 8  illustrates an example flowchart for Recovery Control  512 . 
         [0125]    Step  512 - 2 : The Storage Management Server  500  checks if a path failure has occurred. If there is no failure then the storage management server exits the recovery control process. 
         [0126]    Step  512 - 3 : The Storage Management Server  500  checks the progress of the migration for the failed path. If the migration has finished, proceed to Step  512 - 4 , otherwise Step  512 - 5 . 
         [0127]    Step  512 - 4 : The Migration Source Storage Subsystem  300  creates a virtual port which connects to the active path blockage. The Storage Management Server  500  informs the user to remove a virtual port on Host Computer  100  which connects to the active path. After the removal of the virtual port of the host computer, the Storage Management Server  500  order the Migration Source Storage Subsystem  300  to remove the virtual port. 
         [0128]    Step  512 - 5 : The Storage Management Server  500  allows the migration to continue and exit recovery control. 
         [0129]      FIG. 9-16  illustrates the procedures of the migration. Specifically,  FIG. 9  illustrates an example procedure of introducing the Migration Source Storage  300  to start the migration procedure. 
         [0130]    Procedure P 1 : The Operator  1  sets the port configuration of Port  301   a  and  301   b , for example the security and QoS setting, by using Port Management  311 . 
         [0131]    Procedure P 2 : The Port Management  311  configures the setting of Port  301   a  and  301   b  based on the port configuration. 
         [0132]    Procedure P 3 : The Operator  1  makes new LU  320   a  and  320   b  sharing same Logical Volume  321  by using Volume Management  312 . 
         [0133]    Procedure P 4 : The Volume Management  312  provisions Logical Volume  321  and LU  320   a  and  320   b  with configured setting. 
         [0134]    Procedure P 5 : The Operator  1  sets the configuration of HBA  101   a  and  101   b  to OS  112 . 
         [0135]    Procedure P 6 : The OS  112  runs the HBA Driver  113   a  and  113   b  for HBA  101   a  and  101   b.    
         [0136]    Procedure P 7 : The Operator  1  sets the Multi Path Management  111  to sets the device file and path. 
         [0137]      FIG. 10  illustrates an example procedure for introducing the Migration Target Storage  400 . 
         [0138]    Procedure Q 1 : The Operator  1  sets the port configuration of Port  402   a  and  402   b  by using Port Management  411 . 
         [0139]    Procedure Q 2 : The Port Management  411  configures the setting of Port  402   a  and  402   b  based on the port configuration, and finds LU  320   a  and  320   b  after logging-in. 
         [0140]      FIG. 11  further illustrates the procedure from Step  511 - 2  to Step  511 - 11 . 
         [0141]    Procedure R 1 : The Operator  1  starts the migration by issuing an order to Storage Migration Management  511 . 
         [0142]    Procedure R 2 : The Storage Migration Management  511  orders the Port Management  311  to set virtual target ports on Port  301   a  and  301   b.    
         [0143]    Procedure R 3 : The Port Management  311  sets virtual target ports on Port  301   a  and  301   b.    
         [0144]    Procedure R 4 : The Storage Migration Management  511  orders the Volume Management  312  to provision new LU  320   c  and  320   d  which relate to the same Logical Volume  321  that LU  320   a  and  320   b  have. 
         [0145]    Procedure R 5 : The Volume Management  312  provisions new LU  320   c  and  320   d  and makes a relationship with Logical Volume  321  and virtual target ports on Ports  301   a  and  301   b.    
         [0146]    Procedure R 6 : The Storage Migration Management  511  tells the Operator  1  to change the configuration of Host Computer  100 . 
         [0147]    Procedure R 7 : The Operator  1  changes the HBA configuration on OS  112  to set new virtual initiator pots on HBA  101   a  and  101   b.    
         [0148]    Procedure R 8 : The OS  112  sets new virtual initiator ports on HBA  101   a  and  101   b.    
         [0149]    Procedure R 9 : The OS  112  starts HBA Driver  113   c  and  113   d  for the new virtual initiator ports on HBA  101   a  and  101   b.    
         [0150]    Procedure R 10 : The Operator  1  orders the Multi Path Management  111  to set the device file and path for the new virtual initiator ports on HBA  101   a  and  101   b.    
         [0151]    Procedure R 11 : The Operator  1  informs the Storage Migration Management  511  to end the host computer operation. 
         [0152]      FIG. 12  further illustrates the procedure related to Step  511 - 12 . 
         [0153]    Procedure S 1 : The Storage Migration Management  511  orders the Port Management  311  to stop the existing (not virtual) target ports on Port  301   a  and  301   b.    
         [0154]    Procedure S 2 : The Port Management  311  makes Port  301   a  and  301   b  log-out except for the virtual target ports. 
         [0155]    Procedure S 3 : The Storage Migration Management  511  orders the Volume Management  312  to remove LU  320   a  and  320   b.    
         [0156]    Procedure S 4 : The Volume Management  312  deletes LU  320   a  and  320   b.    
         [0157]      FIG. 13  further illustrates the procedures related to Step  511 - 13  and Step  511 - 17 . 
         [0158]    Procedure T 1 : The Storage Migration Management  511  orders the Port Management  411  to set new virtual target ports on Port  401   a  and  401   b . The new virtual target ports have the same name of the removed ports on Port  301   a  and Port  301   b.    
         [0159]    Procedure T 2 : The Port Management  411  sets the virtual target ports on Port  401   a  and  401   b.    
         [0160]    Procedure T 3 : The Storage Migration Management  511  orders the External Volume Control  413  to provision LU  420   a  and  420   b  with an external volume function to transfer I/O to LU  320   c  and  320   d.    
         [0161]    Procedure T 4 : External Volume Control  413  provisions LU  420   a  and  420   b  with external volume function to transfer I/O to LU  320   c  and  320   d.    
         [0162]      FIG. 14  further illustrates the procedures related to Steps  511 - 18  to  511 - 22 , and Step  414 - 2 - 2 . 
         [0163]    Procedure U 1 : The Storage Migration Management  511  tells the Operator  1  to change the configuration of Host Computer  100 . 
         [0164]    Procedure U 2 : The Operator  1  deletes the paths between the virtual initiator ports on HBA  101   a / 101   b  and the virtual target ports on Port  301   a / 301   b  from the Multi Path Management  111 . 
         [0165]    Procedure U 3 : The Operator  1  deletes the virtual initiator ports on HBA  101   a  and  101   b  by using OS  112 . 
         [0166]    Procedure U 4 : The OS  112  stops HBA Driver  113   c  and  113   d.    
         [0167]    Procedure U 5 : The OS  112  deletes virtual initiator ports on HBA  101   a  and  101   b.    
         [0168]    Procedure U 6 : The Operator  1  informs the Storage Migration Management  511  of the completion of changing the configuration for Host Computer  100 . 
         [0169]    Procedure U 7 : The Storage Migration Management  511  orders the Data Migration  414  to start the migration process. 
         [0170]    Procedure U 8 : The Data Migration  414  copies data from Logical Volume  321  to Logical Volume  421 . 
         [0171]      FIG. 15  further illustrates the procedure related to Step  414 - 2 - 3 . 
         [0172]    Procedure V 1 : The Data Migration  414  orders the External Volume Control  413  to suspend LU  420   a  and  420   b.    
         [0173]    Procedure V 2 : The External Volume Control  413  suspends LU  420   a  and  420   b.    
         [0174]    Procedure V 3 : The Data Migration  414  orders the Volume Management  412  to change the configuration of LU  420   a  and  420   b  to share Logical Volume  421 , and restart LU  420   a  and  420   b.    
         [0175]    Procedure V 4 : The Volume Management  412  sets LU  420   a  and  420   b  to share Logical Volume  421  and restarts the LUs. 
         [0176]      FIG. 16  further illustrates procedures conducted after Step  511 - 23 . 
         [0177]    Procedure W 1 : The Storage Migration Management  511  informs the Operator  1  of the completion of the migration. 
         [0178]    Procedure W 2 : Operator  1  removes Migration Source Storage Subsystem  400 . 
         [0179]      FIG. 17  further illustrates the sequence of the migration in relation to  FIGS. 9 to 16 . In particular,  FIG. 17  illustrates an exemplary sequence of the migration with respect to the Host Computer  100 , Storage Management Server, Source Storage  300 , Target Storage  400 , and Switch  200 , and the interaction of each of those units during the migration. 
         [0180]      FIG. 18  illustrates another possible physical and logical configuration of the system according to embodiments of the invention. In this configuration, a Host Management Server  600  is utilized. The Host Management Server  600  is connected to the Host Computer  100  and the Storage Management Server  500 . Host Management Server  600  has Port Management  611 . The Port Management  611  can manage the server port setting by communicating to the OS  112  and the Multi Path Management  111 . The Port Management  600  can receive the necessary requirements from the Storage Migration Management  511  and return the result. 
       Second Embodiment 
       [0181]      FIG. 19  illustrates an example flowchart for the Port Management  611 . 
         [0182]    Step  611 - 2  and Step  611 - 3 : The Host Management Server  611  checks the received request. If it is a provisioning request, the process proceeds to Step  611 - 3 . If it is a delete request, the process proceeds to Step  611 - 4 . 
         [0183]    Step  611 - 3 : The Host Management Server  611  orders the OS  112  to make virtual initiator ports on HBA  101   a  and  101   b,  and run HBA Driver  101   c  and  101   d . Also, the Host Management Server  611  may order the Multi Path Management  111  to set new paths for the virtual initiator ports. 
         [0184]    Step  611 - 4 : The Host Management Server  611  orders the Multi Path Management  111  to delete paths of the virtual initiator ports. The Host Management Server  611  may further order the OS  112  to stop HBA Driver  101   c  and  101   d,  and delete virtual initiator ports from HBA  101   a  and  101   b.    
         [0185]      FIG. 20  illustrates the migration sequence for an environment utilizing the Host Management Server  600 . The configuration operation for Host Computer  100  is relocated to the Host Management Server  600  from Operator  1 . 
       Third Embodiment 
       [0186]    In the first embodiment, a new path is established between the Migration Source Storage  300  and Host Computer  100 , in the third embodiment, at least two new paths are established between the Migration Target Storage System  400  and Host Computer  100  before terminating a path between the source storage system and the host. Although the new paths are established between the Host Computer and the Migration Target Storage System, redundancy can still be obtained between the Host and the Migration Source Storage System. This can be achieved, for example, by creating temporal LUs in the Migration Source Storage System, mounting the temporal LUs to the Migration Target Storage System, and then establishing paths to the mounted LUs of the Migration Target Storage System. Should one of the new paths fail, one of the remaining new paths maintains the redundancy between the Host and the Migration Target Storage System, and thereby to the Migration Source Storage System via the mounted LUs. The mounted LUs can be removed after migration is completed. An exemplary illustration of this process along with the differences between the first and third embodiments are shown in  FIGS. 21 to 24 . 
         [0187]      FIG. 21  illustrates an exemplary alternative flowchart for Storage Migration Management  511 . 
         [0188]    Step  511 - 2 : The Storage Management Server  500  gathers the configuration information from the Migration Source Storage Subsystem  300 . 
         [0189]    Step  511 - 3 : The Storage Management Server  500  sends the path information to Port Management  411  to establish a path from Ports  402   a  and  402   b  to Ports  301   a  and  301   b.    
         [0190]    Step  511 - 4  and Step  511 - 5 : The Storage Management Server  500  waits for the establishment of the path. If the path isn&#39;t established, notify user to check the condition of the cables or the security setting. 
         [0191]    Step  511 - 6 - 1 : The Storage Management Server  500  orders the Port Management  411  to set new virtual target ports on Port  401   a  and  401   b.    
         [0192]    Step  511 - 7 - 1 : The Storage Management Server  500  orders the Volume Management  412  to provision new LUs  420   c  and  420   d,  using the new virtual target ports on Ports  401   a  and  401   b,  and to mount the Logical Volume  321  of LU  320   a  and  320   b  via the initiator ports  402   a  and  402   b.    
         [0193]    Step  511 - 8 - 1 : The Storage Management Server  500  orders the new virtual target ports on Port  401   a  and  401   b  to log in the fabric. 
         [0194]    Step  511 - 9 - 1 : The Storage Management Server  500  informs the Operator  1  to make new connections from the Host Computer  100  to the new virtual (temporal) target ports on Port  401   a  and  401   b.    
         [0195]    Step  511 - 10  and Step  511 - 11 : The Storage Management Server  500  waits for the completion of the path establishing from Ports  101   a  and  101   b  to the new virtual (temporal) target ports on  401   a  and  401   b.  During these steps, Operator  1  sets new virtual initiator ports on Port  101   a  and  101   b,  runs HBA Drivers  113   c  and  113   d  for the new virtual initiator ports, and registers the virtual initiator port to Multi Path Management  111 . 
         [0196]    Step  511 - 12 : The Storage Management Server  500  orders the Port Management  311  to log out the target ports on Port  301   a  and  301   b.  Additionally, the Storage Management Server  500  may order the Port Management  311  to delete the name of the target ports on Port  301   a  and  301   b.    
         [0197]    Step  511 - 13 : The Storage Management Server  500  orders the Port Management  411  to name the deleted name as virtual target ports to Port  401   a  and  401   b.    
         [0198]    Step  511 - 14 : The Storage Management Server  500  orders the Extended Volume Control  413  to make new LUs as external volumes mounting LU  320   c  and  320   d.    
         [0199]    Step  511 - 15 : The Storage Management Server  500  orders the Port Management  411  to log in the virtual target ports on Port  401   a  and  401   b.    
         [0200]    Step  511 - 16  and Step  511 - 17 : The Storage Management Server  500  waits for the establishment of the path. During Step  511 - 12  and Step  511 - 14 , the path between Ports  101   a / 101   b  and  301   a / 301   b  is active because of the path between the respective virtual ports. 
         [0201]    Step  511 - 18 : The Storage Management Server  500  informs the Operator  1  to terminate the virtual initiator ports on Port  101   a  and  101   b.    
         [0202]    Step  511 - 19  and Step  511 - 20 : The Storage Management Server  500  waits for the completion of the logging-out of the virtual initiator ports on Port  101   a  and  101   b.    
         [0203]    Step  511 - 21 : The Storage Management Server  500  orders the Data Migration  414  to migrate data and configuration from Logical Volume  321  to  421 . 
         [0204]    Step  511 - 22 - 1 : After the migration is finished, the Migration Target Storage Subsystem  400  deletes the virtual (temporal) target ports on Port  401   a  and  401   b.    
         [0205]    Step  511 - 23 : The Storage Management Server  500  informs the user to remove Migration Source Storage Subsystem  300 . 
         [0206]      FIG. 22  further illustrates the procedure during Step  511 - 2  to Step  511 - 11 . 
         [0207]    Procedure R 1 : The Operator  1  starts the migration by issuing an order to Storage Migration Management  511 . 
         [0208]    Procedure R 2 - 0 : The Storage Migration Management  511  orders the Port Management  311  to set virtual target ports on Port  301   a  and  301   b.    
         [0209]    Procedure R 2 - 1 : The Storage Migration Management  511  orders the Port Management  411  to set virtual target ports on Port  401   a  and  401   b.    
         [0210]    Procedure R 3 - 0 : The Port Management  311  sets virtual target ports on Port  301   a  and  301   b.    
         [0211]    Procedure R 3 - 1 : The Port Management  411  sets virtual target ports on Port  401   a  and  401   b.    
         [0212]    Procedure R 4 - 0 : The Storage Migration Management  511  orders the Volume Management  312  to provision new LU  320   c  and  320   d  which relate to the same Logical Volume  321  that LU  320   a  and  320   b  have. 
         [0213]    Procedure R 4 - 1 : The Storage Migration Management  511  orders the Volume Management  412  to provision new LU  420   c  and  420   d  which mounts the LU  320   c  and  320   d  via the Ports  402   a  and  402   b.    
         [0214]    Procedure R 5 - 0 : The Volume Management  312  provisions new LU  320   c  and  320   d  and makes a relationship with Logical Volume  321  and virtual target ports on Ports  301   a  and  301   b.    
         [0215]    Procedure R 5 - 1 : The Volume Management  412  provisions new LU  420   c  and  420   d  mounting LU  320   a  and  320   b  via the Ports  402   a  and  402   b.    
         [0216]    Procedure R 6 : The Storage Migration Management  511  tells the Operator  1  to change the configuration of Host Computer  100 . 
         [0217]    Procedure R 7 : The Operator  1  changes the HBA configuration on OS  112  to set new virtual initiator pots on HBA  101   a  and  101   b.    
         [0218]    Procedure R 8 : The OS  112  sets new virtual initiator ports on HBA  101   a  and  101   b.    
         [0219]    Procedure R 9 : The OS  112  starts HBA Driver  113   c  and  113   d  for the new virtual initiator ports on HBA  101   a  and  101   b.    
         [0220]    Procedure R 10 : The Operator  1  orders the Multi Path Management  111  to set the device file and path for the new virtual initiator ports on HBA  101   a  and  101   b.    
         [0221]    Procedure R 11 : The Operator  1  informs the Storage Migration Management  511  to end the host computer operation. 
         [0222]      FIG. 23  further illustrates the procedure related to Step  511 - 12 . 
         [0223]    Procedure S 1 : The Storage Migration Management  511  orders the Port Management  411  to stop the target ports on Port  301   a  and  301   b.    
         [0224]    Procedure S 2 : The Port Management  311  makes Port  301   a  and  301   b  log-out except for the virtual target ports. 
         [0225]    Procedure S 3 : The Storage Migration Management  511  orders the Volume Management  312  to remove LU  320   a  and  320   b.    
         [0226]    Procedure S 4 : The Volume Management  312  deletes LU  320   a  and  320   b.    
         [0227]      FIG. 24  further illustrates the procedures related to Step  511 - 13  and Step  511 - 17 . 
         [0228]    Procedure T 1 : The Storage Migration Management  511  orders the Port Management  411  to set new virtual target ports on Port  401   a  and  401   b . The new virtual target ports have the same name of the removed ports on Port  301   a  and Port  301   b.    
         [0229]    Procedure T 2 : The Port Management  411  sets the virtual target ports on Port  401   a  and  401   b.    
         [0230]    Procedure T 3 : The Storage Migration Management  511  orders the External Volume Control  413  to provision LU  420   a  and  420   b  with an external volume function to transfer I/O to LU  320   c  and  320   d.    
         [0231]    Procedure T 4 : External Volume Control  413  provisions LU  420   a  and  420   b  with external volume function to transfer I/O to LU  320   c  and  320   d.    
         [0232]    Moreover, other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. Various aspects and/or components of the described embodiments may be used singly or in any combination in the computerized storage system preventing a single point of failure. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.