The present invention relates generally to storage device systems with increased usability adaptable for use with hand-carriable storage media. More particularly, but not exclusively, the invention relates to memory device systems with redundancy at respective constituent elements for improvement of usability.
In computer systems a document known as Patterson""s paper has been known as one of the prior art documents most pertinent to the invention.
A.C.M. SIGMOD Conference Proceeding, xe2x80x9cA Case for Redundant Arrays of Inexpensive Disks (RAID)xe2x80x9d by D. Patterson et al., Chicago, Ill., Jun. 1-3, 1988 at pp. 109-116.
The Patterson paper discloses therein one technique relating to data distribution/layout on disk arrays.
Disk array is a mechanism for attainment of high performance with increased reliability of disk systems. In such disk array, enhanced performance may be attainable by forcing processor devices to recognize a plurality of physical disks as a single xe2x80x9cvirtualxe2x80x9d disk device. On the other hand, for achievement of higher reliability, redundant data for use in recovering data as accidentally destructed upon occurrence of failure or malfunction in data storage disk devices is prestored in a separate disk device(s). Generally, one segment of data used as a unit for read/write operations of disk devices is called the xe2x80x9crecordxe2x80x9d among those skilled in the art; in this respect, the Patterson paper has proposed several record layout methods. Note here that where disk arrays are employed, it can happen in some cases that the xe2x80x9crecordxe2x80x9d acting as the read/write unit when viewed from the host computer is different in data length from the xe2x80x9crecordxe2x80x9d as actually recorded in disk devices, namely, a record as stored at a single sector of disks. The former will be referred to as xe2x80x9clogical record,xe2x80x9d whist the latter as xe2x80x9cphysical recordxe2x80x9d hereinafter. Now, record layout methods as disclosed in Patterson""s paper will be explained below.
One typical record layout scheme is to store logical recordsxe2x80x94i.e. those records as viewed from the processor device sidexe2x80x94in a way such that these are subdivided for storage into a preselected number (say xe2x80x9cmxe2x80x9d; here m is the integer greater than or equal to 1) of physical records on disk devices. This approach will be called the xe2x80x9cdivisional layoutxe2x80x9d method. With such a divisional layout scheme, the same effect may be obtainable as would be attained when the data transfer rate is virtually increased by m times because of the capability of transferring a single logical record between or among m disk devices operatively associated therewith. Then, a redundant data preparation method in the divisional record layout scheme will be explained as follows. In the divisional layout, for m physical records as divided from a logical record, a plurality ofxe2x80x94xe2x80x9cnxe2x80x9d where n is the integer more than 1xe2x80x94redundant data items are prepared for storage in respective disk devices as a single physical record with respect to one disk device (n records as a whole). Hereinafter, those physical records storing therein certain data directly accessible by the processor device for reading/writing will be referred to as xe2x80x9cdata recordsxe2x80x9d whereas other physical records storing redundant data as xe2x80x9cparity records.xe2x80x9d Further, a combination of m data records and n parity records as organized together into a group will be called the xe2x80x9cparity group.xe2x80x9d Typically, if n parity records are within the parity group, data of such parity group may be recovered even upon occurrence of operation failures or disturbances in disk devices as far as the number thereof is less than or equal to n.
Another Patterson""s record layout scheme proposed is to store a logical record acting as the read/write unit as looked at from the processor device functionally supervising disk devices as a single physical record, i.e. a single data record. This approach will be called the xe2x80x9cnon-divisional layoutxe2x80x9d scheme hereinafter. Accordingly, logical records are equivalent to data records. (Since respective physical records are assigned with either data records or parity records, the physical records will not always remain exactly equal to logical records. In other words, while a single logical record is one physical record, it is not always true that one physical is a single logical record and can be a parity record in several cases.) One noticeable feature of the non-divisional layout scheme lies in that read/write processings are executable for every one of respective disk devices. (With the divisional layout scheme, it should be required that plural disk devices be exclusively dedicated or xe2x80x9cslavedxe2x80x9d during execution of read/write operations.) As a consequence, with the non-divisional layout scheme, it becomes possible to improve the multiplexibility or xe2x80x9cmulti-taskingxe2x80x9d offerability of read/write processings to be executed within disk arrays, which in turn leads to capability of achieving enhanced performance. With this non-divisional layout scheme also, n parity records are prepared from m data records for storage in disk devices. Note however that while the divisional layout scheme is designed to use a collection of data records within a parity group to form a single logical record as viewed from the processor device, the non-divisional layout scheme treats a respective one of data records as if it were a complete independent logical record when looking at from the processor device.
In computer systems, magnetic tape drives or optical storage drives or equivalents thereto are frequently employable as data storage devices other than the disk devices. Especially in recent years, digital versatile disks (dvds) are becoming more important in the manufacture of advanced computer systems. One significant feature of these storage devices of the types mentioned above is that storage media or record carrier bodies are separated in structure from read/write (R/W) devices operatively associated therewith, and that one storage medium is loaded into any desired R/W device for permitting execution of reading data therefrom or writing data thereinto. These media are generally known as hand-carriable media. In large-scaled computer systems a library unit is introduced in order to readily accomplish management of an extremely great number of carriable storage media. The library may include, in addition to storage media and R/W devices, a containment or xe2x80x9crackxe2x80x9d structure for housing therein an increased number of storage media, and a computer-controlled robot module for carrying and delivering storage media between the rack and R/Ws. In the computer systems with such library architecture, an appropriate library management software unit is typically provided on a supervisory or xe2x80x9chostxe2x80x9d computer used. The library management in this case is for managing the system to monitor or xe2x80x9cwatchxe2x80x9d which type of storage medium is present to store what kind of information. To this end, an ordinary approach upon loading a new storage medium or media is to let the host computer become aware of occurrence of such new media loading event by sending a corresponding notice thereto.
Recently, data to be processed by computer systems increases in scale more and more; thus, achievement of its usability and maintenance flexibilityxe2x80x94this may also be called xe2x80x9cavailabilityxe2x80x9d among those skilled in the computer artxe2x80x94is required more strictly. Therefore, in storage device systems including the aforesaid carriable recording media also, it remains effective to attain enhanced usability by incorporating therein the concepts as proposed by the Patterson paper discussed supra.
One prior known architecture applying such concepts to carriable storage media is described, for example, in Alan E. Bell (IBM Research Division), DVD Applications, COMDEX ""96, Nov. 20, 1996. This Bell document has proposed redundant arrays of inexpensive libraries (RAIL) with redundancy employing a combination of plural sets of currently available standard libraries including dvds, R/W devices, robot modules, and others.
With regard to data recovery/restore technology, one typical prior art technique of repairing destructive data is disclosed in U.S. Pat. No. 4,914,656 wherein a storage device system having multiple disk arrays with redundancy is configured such that upon occurrence of operation failure or malfunction in one disk device, resultant destructive data is restored for writing on a spare disk device(s) under management of the entire system, rather than on the individual one of disk arrays in a way independent of one another.
The disk array technology with redundancy configuration as proposed by the Patterson""s paper stated previously may also be applicable to the library unit using carriable media. When this is done, those disk drive units constituting a disk array may correspond to carriable media and R/W devices, each of which is with redundancy configuration.
In the library unit with such redundancy configuration, it might be obvious and natural in view of the inherent structure of library unit that spare carriable storage media are provided inside the library unit for future alternative use when any one of xe2x80x9cnativexe2x80x9d carriable media malfunctions. This in turn means that such spare carriable media are inherently the ones that will be used in a manner such that the library unit makes use of them independently of the host computer.
Where such spare carriable media are also loaded into the library unit, a need arises to avoid notifying library management part of the host computer of occurrence of storage media loading events. This is required because of the fact that otherwise, the host computer can behave badly to attempt to use such spare media for data storage, which would result in lack of necessary storage media for use in restoring destructive data on a malfunctioning carriable media in accidental operation failure events.
It is therefore an object of the present invention to provide an improved data storage method and apparatus capable of avoiding the problems faced with the prior art.
It is another object of the invention to provide a data storage distribution scheme adaptable for use in computer-controlled library unit with redundancy configuration capable of increasing performance and efficiency as well as reliability.
It is yet another object of the invention to provide library unit with redundancy capable of increasing usability by, upon loading a spare carriable storage medium, temporarily eliminating notifying a host computer of loading the spare storage medium thereinto.
It is a further object of the invention to provide library unit with redundancy capable of maximizing usability by forcing the host computer to ignore any notification as sent thereto upon loading spare storage media thereinto.
To attain the foregoing objects the present invention disclosed and claimed herein provides library unit including standard carriable storage media which stores therein one of data to be sent to or written from a host computer and redundancy data generatable from the data. The apparatus also includes a spare carriable storage medium for use upon occurrence of malfunction of the standard storage medium. A specific device is provided for recognizing spare carriable storage media as mere spare ones. The device is operable to eliminate issuance of a notice or report to the host computer when the spare carriable storage medium is loaded thereinto. Elimination of issuing to the host computer any notice indicating occurrence of spare media loading events may enable the host computer to be kept silent about occurrence of such events.
In accordance with one aspect of the instant invention, library unit includes standard carriable storage media for storage of one of data to be transferred to or written from a host computer and redundancy data generatable from the data. A spare carriable storage medium is employed for use device responsive to instructions from the host computer for performing data recording and reproduction operations. The apparatus further includes a media loader device for loading a standard physical medium storing therein data as written by the physical R/W device along with redundancy data of the data and a spare physical medium for use upon occurrence of malfunction of one or several of the standard physical media. A rack is provided in the apparatus, which has a standard media storage space for storing a physical medium loaded and a spare media storage space. The media carrying robot is configured to store into the rack the spare physical medium as loaded into the media loader device. A device is provided for distinguishing the loaded spare physical medium from the standard physical media.
In accordance with other aspect of the invention, a computer system including a host computer arranged to instruct its associated library unit or unit to load more than one carriable storage medium into it, any spare carriable storage media as loaded thereinto may be regarded as mere spare storage media without the need for receipt of instructions from the host computer while simultaneously preventing any relevant report from being sent to the host computer even after completion of such media loading. Alternatively, even where such report could be issued to the host computer, let the computer ignore this report.
In a computer system with its library unit as designed to report to the host computer that a carriable storage media has been loaded thereinto every time this event takes place, users are permitted to manually designate a spare carriable media-loading mode thus enabling recognition of any one of those carriable media loaded in the spare media loading mode as a mere spare one while rendering the host computer kept silent about occurrence of such media loading events. Or alternatively, although reporting to the host computer that such is a spare medium, let the computer recognize it as the spare one and then ignore this report.
These and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.