Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
1998-01-09
2001-01-09
Cabeca, John W. (Department: 2752)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
C711S004000, C711S100000, C711S112000
Reexamination Certificate
active
06173360
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the transfer of data between a system using one type of interface to an external storage system using a different type of interface. More particularly, the invention relates to a converter that allows an existing extended-count-key-data storage system to be used as a storage device for a SCSI-type interfaced open host system.
2. Description of the Related Art
A direct access storage device (DASD) comprises one or more movably mounted disks coated with remnant magnetic material. Either fixed block or variable length records are recorded along circular track extents formatted on the disks. The tracks are concentric such that a movable arm with a READ or WRITE head or a switchable set of fixed heads must be positioned or activated over the desired track to effectuate transfer of the records to or from the disk. In an assembly of disks, the set of all tracks that can be accessed without repositioning the access mechanism is termed a “cylinder”. Where a DASD stores 500 tracks per disk, there would be 500 cylinders. The cylinders may be grouped in logical or arbitrary sets. Contiguous cylinders are grouped together to form “bands” such that cylinders
0
-
10
might be a first band, and
11
-
100
a second band. Efficient data movement frequently has required bulk transfer, that is, staging a track's worth of data or even a cylinder's worth of data at a time, to another level of storage.
There is no connection between the logical organization of data such as datasets and their counterpart cylinder and track location in DASD storage. For some purposes, such as reducing READ data transfer time, it is advantageous to store the dataset records in contiguous tracks or cylinders. For other purposes, such as batch DASD recordation of random WRITE updates of records, the writing might be to contiguous DASD storage so that each record written would be remote from other records in the same dataset stored elsewhere in DASD.
Another level of storage common to DASD environments is virtual storage (VS). A VS device may comprise a single DASD using multiple disks or several DASDs where each employs one or more disks. Regardless, the allocation of data to the VS is coordinated by a special controller contained in the VS device or a host system/subsystem to which the VS system is connected. An implementation of VS could comprise a system using count-key-data (CKD) or extended-count-key-data (ECKD). The controller generally determines where data will be stored. For example, the controller decides which disk of the VS device will receive the data. By using a separate controller to allocate data to the various disks, precious host processor time is freed up for other purposes. As far as the host processor is concerned, the VS device appears to be one disk. One example of such an arrangement, hereafter referred to as a virtual storage system (VSS), is where the VS device or system is coupled to an ECKD system such as an IBM 3990 system—manufactured by the assignee of the current invention.
Commonly, the interface between a VSS system and a host system to which it may be connected is uniform. For example, a host system using a SCSI-type interface internally will usually be connected to a VSS system using a SCSI-type interface. However, certain types of conventional high end data processing equipment, deemed enterprise, may use a different channel-to-control-unit input/output (I/O) interface using fiber or optical cables as a transmission medium. This type of enterprise system connection, deemed “ESCON,” may be found, for example, on a RAMAC multiple disk array. ESCON may also be used in connecting an MVS system to or within the VSS.
However, an ESCON interface used by the VSS precludes the use of VSS with “open” systems. An open system is a system whose characteristics comply with standards made available throughout the industry—such as SCSI-types, IDE, or EIDE—and that therefore cannot be connected to other systems not complying with the same standard. Simply put, it currently is not possible to connect an open host system utilizing an open interface with a VSS. What is needed is an apparatus and method that would allow a high end VSS to be attached to a host open system, thereby allowing the VSS to act as extended “open” storage for the open host system.
SUMMARY OF THE INVENTION
Broadly, the present invention concerns a converter system that allows an open host system using a first interface to use a second storage system using a second interface.
In one embodiment, the invention may be implemented to provide a conversion method to allow a VSS using an ESCON interface to be used by an open host system using an open interface without necessitating changes to the VSS or the open host interfaces. In another embodiment, the VSS also may perform the volume management of an associated MVS system. If the open host system employs a SCSI-type interface, then the method permits the open system to be physically located greater than 25 meters from the VSS.
In one embodiment, the method involves mapping the SCSI-type interface data and commands into parameters used and understood by the VSS. For example, the command sets used with a SCSI-type connection are very different from the command sets used with an ESCON connection. In one embodiment, when data is transferred from the open host SCSI-system to the VSS ESCON storage, the method of the present invention maps the SCSI-type command set used by the host into a command set understandable by the VSS ESCON storage.
In another embodiment, the invention may be implemented to provide an apparatus including a hard drive and a processor communicatively coupled to a storage unit, wherein the processor executes the method steps discussed above. The apparatus may also include an input/output (I/O) interface and an I/O line, such as a bus, cable, electromagnetic link, or other means for exchanging data between the processor, the storage unit, and an external storage unit.
In still another embodiment, the invention may be implemented to provide an article of manufacture comprising a data storage medium tangibly embodying a program of machine-readable instructions executable by a digital data processing apparatus to perform method steps for translating the first-type interface parameters into second-type interface parameters used and understood by the VSS.
The preferred embodiments of the present invention afford its users with a number of distinct advantages. For one, the converter system allows a high end VSS employing ECKD formatted DASDs to be attached to an open host system. This provides the open system with an ESCON backup system that can also be used to restore the host open system in case of a host system failure or any other condition that prevents access to requested data.
Furthermore, the invention in its various embodiments also provides a number of other advantages and benefits, which should be apparent from the following description of the invention.
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Beardsley Brent Cameron
Day III Kenneth Fairclough
Hartung Michael Howard
Micka William Frank
Bataille Pierre-Michel
Cabeca John W.
Dan Hubert & Asscoc.
International Business Machines - Corporation
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