Method and system for dynamically reassigning unused logical volumes from a storage subsystem to an open systems host

[0002] The present invention relates to storage subsystems, and more particularly to a method and system for dynamically reassigning unused logical volumes on a storage subsystem to an open systems host.

[0003] Mainframe computers typically utilize a storage subsystem for storing and accessing huge amounts of data. The storage subsystem is commonly implemented as a direct access storage system (DASD) where many hard disks are organized as a redundant array of inexpensive disks (RAID). The RAID-5 storage architecture, for example, stores data by spreading it over multiple disks along with parity information. If a single disk fails, the parity information allows the system to regenerate that lost data quickly and transparently without interrupting online processing. To the mainframe, a typical storage subsystem RAID data space is one large data space that is accessed through logical volumes.

[0004] As data availability needs increase, users see the advantages in making the storage subsystem available not only to mainframe computers, but also to open systems hosts, such as PC's or workstations running Unix and Windows NT operating systems, for instance. The open systems hosts are connected to the storage subsystem through SCSI (Small Computer System Interface) host adapters, or SCSI controllers. The operating systems of most open systems hosts, however, cannot handle the large data spaces provided by logical volumes. Therefore, on the open systems hosts side, the storage subsystem's data space is divided into multiple SCSI logical unit numbers (LUNs).

[0005] The benefits of making the storage subsystem available to open systems hosts are that it allows large enterprises to consolidate open systems servers into a single location under similar IT (information technology) management, and allows open systems servers to take advantage of advanced storage functions. However, due to the complexities of server consolidation and new enterprise application development, it is very difficult to plan disk storage capacity requirements for the open systems hosts. Consequently, there may be logical volumes on the mainframe side of the storage subsystem that are not used. In order for the open systems host to access this untapped storage space, these unused logical volumes must be reassigned to open systems host LUNs.

[0006] Reassigning unused logical volumes from the storage subsystem to the open systems host LUNs has traditionally required temporarily suspending any software processes in the system that will be affected by the reassignment. This includes any software processes on the storage subsystem and mainframe host that access the logical volumes to be reassigned, as well as any software processes on the open systems host that are to be given access to the reassigned logical volumes. After a check is made that the software processes are not currently modifying any data, the software processes are suspended and an operator manually reconfigures both the mainframe and the open systems host. Suspending the processes of a large enterprise system in this manner and making the system unavailable to clients is not only disruptive and inefficient, but also costly.

[0007] Accordingly, what is needed is a method and system for dynamically reassigning unused logical volumes on a storage subsystem to an open systems host. The present invention addresses such a need.

[0008] The present invention provides a method and system for reassigning unused logical volumes on a storage subsystem to an open systems host that uses logical unit numbers (LUNs). The storage subsystem and the open systems hosts execute respective software processes, and the open systems host is connected to a storage subsystem via an adapter that is controlled from a support controller. The method and system include sending a communication message from the support controller to the adapter, wherein the communication message reassigns the unused logical volumes to LUNs. The method and system further include updating a logical-to-physical mapping stored within the adapter in response to receiving the communication message, whereby storage capacity of the open systems host is increased without suspending the software processes.

[0009] According to the method and system disclosed herein, reconfiguring the system with real-time messaging provides enterprises with a flexible and cost effective method for using excess storage-subsystem capacity in support of open systems hosts.

[0010] FIG. 1 is a block diagram illustrating the operating system environment for the present invention.

[0011] FIG. 2 is a flow chart illustrating the process of dynamically reassigning unused logical volumes on a storage subsystem to an open systems host using real-time messaging in accordance with the present invention.

[0012] FIGS. 3A-3D are diagrams illustrating different ways of reassigning logical volumes 24 to open systems host LUNs via messaging.

[0013] The present invention relates to a process for dynamically reassigning unused logical volumes to open systems LUNS. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein.

[0014] FIG. 1 is a block diagram illustrating the system environment for the present invention. A storage subsystem 10 is implemented as a direct access storage system (DASD) where hard disks are organized as a redundant array of inexpensive disks (RAID) 12. The storage subsystem 10 is accessed by both a mainframe host computer 14 and an open systems host 18. In a preferred embodiment, the mainframe host 14 uses operating systems such as Multiple Virtual Storage/Extended Architecture (MVS/XA) and Virtual Machine (VM), while the open systems host uses operating systems such as Unix and Windows NT.

[0015] The storage system 10 also includes SCSI host adapters 16a, for enabling one or more open systems host 18 to access the storage subsystem 10, and one or more mainframe host adapters 16bfor enabling the mainframe host 14 to access the storage subsystem 10. The host adapters 16aand 16binclude their own microprocessor (e.g., Motorola 2900) and memory for controlling the transference of data.

[0016] A PC-based system referred to as a support controller 20 is connected to the storage subsystem 10 that enables an operator to configure and administer the storage system 10. The support controller 20 and the host adapters 16aand 16brun a common operating system for compatibility and communication. In a preferred embodiment of the present invention, the support controller 20 and the host adapters 16aand 16buse the Nucleus Operating System by Accelerated Technology.

[0017] Both the open systems host 18 and the mainframe host 14 can be connected to more than one adapter 16aand 16brespectively (hereinafter adapters 16). From the mainframe host 14 side, the storage system 10 is organized as a series of logical volumes (LV) 24 that map on top of the hard disks. From the open systems host 18, the storage system 10 is organized as a series of SCSI logical unit numbers (LUNs) that map to the logical volumes 24.

[0018] Initially, the operator assigns storage space from the storage subsystem 10 to the open systems host 18 and the mainframe host 14 via a configuration process that maps logical volumes 24 to physical locations on the disk drives in the storage subsystem 10, which is referred to as a logical-to-physical mapping. This logical-to-physical mapping is stored as tables in the respective adapters 16.

[0019] When logical volumes 24 are assigned to the open systems host 18, but go unused by the mainframe host 14 side, it is desirable to reassign the unused logical volumes 24 the open systems host 18. This, however, typically requires suspending any software processes on the storage subsystem 10 and mainframe host 14 that currently access the logical volumes 24 to be reassigned, as well as any software processes on the open systems host 18 that will be given access to the reassigned logical volumes 24.

[0020] The present invention provides a method and system for dynamically reassigning unused logical volumes 24 on a storage subsystem 10 to an open systems host 18 without suspending any software processes on the storage subsystem 10, the mainframe host 14, or the open systems host 18. The reassignment process is accomplished through software by sending the reconfiguration information to the hardware adapters 16, which then updates the configuration tables during system operation More specifically, reassigning unused logical volumes 24 to the open systems host 18 is accomplished by sending real-time communication messages 22 from the system controller 20 to the processes running on the individual adapters 16. According to the present invention, the new configuration information with the data of the newly reassigned logical volumes 24 is entered by an operator at the support controller 20 and sent to the affected adapters 16 through real-time operating system messaging.

[0021] FIG. 2 is a flow chart illustrating the process of dynamically reassigning unused logical volumes 24 on a storage subsystem 10 to an open systems host 18 using messaging in accordance with the present invention.

[0022] The process begins by determining if any unused logical volumes 24 are present on the mainframe host 14 side in step 40, and determining if there is a need on the open systems host 18 for additional storage capacity in step 42. If so, then an operator ensures that the unused logical volumes 24 are disabled in step 44.

[0023] The operator then reconfigures the storage subsystem 10 by sending a message 22 from the support controller 20 to the affected adapters 16 to reassign the unused logical volumes 24 to open systems logical addresses in step 46. For the affected host adapters 16a, the support controller 20 sends a message 22 indicating what additional logical volumes 24 are now available to that particular adapter 16a. For the affected mainframe adapters 16b, the support controller 20 sends a message 22 restricting access to the reassigned logical volumes 24. In response to receiving the message 22, the affected adapters 16 return an acknowledgement in step 48, and update their respective tables that hold the logical-to-physical mappings, such that the unused logical volumes 24 are reassigned to open systems LUNs in step 50.

[0024] According to the present invention, no system software needs to be suspended to reassign unused logical volumes 24 because the host adapters 16 have the capability of receiving and processing messages 22 while handling requests from one or more open systems hosts 18.

[0025] In a preferred embodiment, the messages 22 sent from the support controller 20 to the host adapters 16 have a standard format that includes the following:

[0026] Function code: indicates the purpose of the message

[0027] Destination ID: adapter address

[0028] Source ID

[0029] Path

[0030] Length of message

[0031] Response queue: indicates where adapter is to send acknowledgement

[0032] Response ID

[0033] Flags for additional information

[0034] Data being transferred

[0035] The data being transferred pertains to LUNs, in particular their addresses and sizes:

[0036] Port

[0037] Target ID

[0038] LUN

[0039] Mode

[0040] Primary adapter

[0041] Secondary adapter

[0042] Logical ID

[0043] Logical start cylinder

[0044] Logical end cylinder

[0045] LUN start block

[0046] LUN end block

[0047] The host adapters 16 process this data received from the support controller 20 and update their internal tables with the new information.

[0048] FIGS. 3A-3D are diagrams illustrating example methods of reassigning logical volumes 24 to open systems host LUNs via messaging. FIG. 3A shows an open systems host 18 having two LUNs 60, and a mainframe host 14 having several logical volumes 62, some of which are unused. Examples of logical volumes include an IBM 3390-9 and 3380.

[0049] FIG. 3B shows that the reassignment of the logical volumes 62 from the mainframe host 14 side to LUNs 60 may be one-to-one, in which one logical volume 62 is assigned to a single open systems LUN 64.

[0050] FIG. 3C shows a reassignment of the logical volumes 62 from the mainframe host 14 to the open systems host 18 in which multiple logical volumes 62 are assigned to a single open systems LUN, creating one large LUN 66.

[0051] FIG. 3D shows that a reassignment is also valid within the open systems host 18 itself by reassigning logical volumes 24 from individual LUNs 60 to a different target LUN, creating a single large LUN 68.

[0052] In a further aspect of the present invention, unused LUNs on the open systems host 18 side may also be dynamically reassigned to logical volumes 24 on the storage subsystem 10 for use by the main host 14. The only extra step required is that when that when the LUN's are reassigned as logical volumes 24 after being used as LUN's, the logical volumes 24 need to be reformatted for use by the mainframe host 14. This is accomplished without suspending the host processes by sending messages from the support controller 20 to the affected host adapter 16a, while access to the logical volumes/LUN's from the open systems host 18 is restricted. It should be kept in mind, however, that this reformatting does not need to take place when reassigning a logical volume 24 to a LUN.

[0053] A method and system for reassigning unused logical volumes on a storage subsystem to an open systems host that uses logical unit numbers (LUNs) has been disclosed that increasing the storage capacity of the open systems host without shutting down and disrupting the system. Reconfiguring the system with real-time messaging as described herein provides enterprises with a flexible method for using excess storage subsystem capacity in support of open systems hosts.

[0054] Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one or ordinary skill in the art without departing from the spirit and scope of the appended claims.