Data processing: generic control systems or specific application – Specific application – apparatus or process – Article handling
Reexamination Certificate
2001-09-10
2003-10-21
Tran, Khoi H. (Department: 3651)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Article handling
C700S225000, C711S112000, C360S098010, C369S030060, C369S030280, C369S178010
Reexamination Certificate
active
06636778
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to data storage drives of an automated data storage library which stores portable data storage cartridges in storage shelves and transports the portable data storage cartridges between the storage shelves and the data storage drives for mounting and demounting the portable data storage cartridges at the data storage drives, and, more particularly, to the allocation of those data storage drives.
BACKGROUND OF THE INVENTION
Automated data storage libraries are increasingly employed for storage of large quantities of data, typically data that is infrequently accessed by the host applications. The data is stored on portable data storage cartridges which are stored in storage shelves. Examples of portable data storage cartridges are cartridges containing a length of magnetic tape or containing an optical disk.
When the data is accessed by the library, an accessor robot operated by a robot control of the library, grips the desired portable data storage cartridge from the storage shelf at which it is stored and transports the portable data-storage cartridge between the storage shelves and data storage drives for mounting and demounting the portable data storage cartridges at the data storage drives, and returning the portable data storage cartridge to the same or a different storage shelf.
Automated data storage libraries are sometimes arranged so that, even in the presence of multiple host applications, the library and its data storage drives appear to each host application as its own library and drives. In one example, a specific set of storage shelves and at least one data storage drive of the library is dedicated to each host application. Upon a request for data from the host application, the portable data storage cartridge having the requesting data is accessed by the accessor robot of the library, and delivered to a data storage drive dedicated to the host application for use by the host application. The host application can thus conduct a series of mounts on a known drive. This is very efficient from the standpoint of the host, since its drive is always available, and the drive addressing is direct and immediate. The library may also appear to be directly assigned to the host application, but the accessor robot is actually shared. It is less efficient from the standpoint of the drive usage in that, if each of the host applications is not constantly using its dedicated data storage drive(s), the drives are often idle. Since the drives are assigned to different host applications, any host application that is particularly active is unable to “borrow” drives from another host application, and, for example, if all of the assigned drives are utilized and data on a different cartridge is needed, the host application may have to wait until the host application itself demounts one cartridge or releases its drive in order to access data on the other cartridge. Any “borrowing” of a drive from another host application would require reconfiguring at least the device drivers for both host applications. Should a host application grow in its needs, new drives cannot be assigned to that host application without reconfiguring at least the host application.
In another example, the host applications are not allowed direct communication with a data storage drive. Rather, a “virtual” library is established which employs cache storage (typically disk drives) to store data received from host applications, acting as though the cache storage is a data storage drive and is writing the data to portable data storage cartridge. The data may be reaccessed while in the cache, called a “cache hit”. If not reaccessed, the library downloads the data from the cache storage to a cartridge employing a data storage drive selected by the library. When data is requested by the host application, and it is not in cache, called a “cache miss”, the library employs a table to find the cartridge storing the data, operates the accessor robot to access the cartridge, finds an available data storage drive, operates the accessor robot to mount the cartridge on the drive, reads the data from the cartridge and uploads the data to cache. From the standpoint of the library, the usage of the library components is efficient. However, cache storage is expensive and adds cost and complexity. The cache storage must be sufficiently large to handle large data sets and must have good staging and destaging algorithms to avoid excessive “cache miss” situations. The host applications communicate with the cache rather than directly with a drive, and any host application can contend for use of shared components, leading to less predictable performance.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an automated data storage library system which employs shared components in an efficient manner.
Another object of the present invention is to allow expanding host applications or the library to receive the benefit of additional drives without requiring reconfiguration of the host applications or the library.
An allocation system and computer implemented method are provided for allocating physical data storage drives of an automated data storage library. The library stores a plurality of portable data storage cartridges in storage shelves, and an accessor robot transports the portable data storage cartridges between the storage shelves and the data storage drives for mounting and demounting the portable data storage cartridges at the data storage drives.
The allocation system comprises a drive resource provider coupled to, or of, the library, responsive to the requests for data storage drives, e.g., from host application(s). The drive resource provider assigns a plurality of the library physical data storage drives to a pool, and allocates and deallocates the data storage drives from the pool for the benefit of the host applications, in accordance with the copending '00038-US1 application.
In accordance with the present invention, the drive resource provider, upon receiving a request for a data storage drive when all of the data storage drives of the pool are allocated, indicates to the library to hold any mount of a portable data storage cartridge relative to the request. Additionally, a drive image provider, upon receiving the request when all of the drives are allocated, provides an indication that the requested drive is currently unavailable to complete any subsequent command requiring a mounted portable data storage cartridge. As discussed in the copending '00038-US1 application, the response may comprise a fake completion response called therein “not ready”. Thus, the host application is assured that it has a data storage drive, and, if needed, can retry or issue its next command relative to the drive. If the next command does not require that the drive be ready or that portable data storage cartridge be mounted and ready, the library may be able to handle the command immediately.
The drive resource provider, subsequent to providing the indications, awaits a request for deallocation of a data storage drive and demount of any portable data storage cartridge at the deallocated data storage drive, and allocates the deallocated data storage drive to the request for a drive, and indicates to the library to release the hold of the mount relative to the request.
The drive resource provider additionally assigns at least one of the plurality of library data storage drives as spare drives, outside of the pool. Then, the drive resource provider, subsequent to providing the indications, allocates one of the at least one spare drives to the request, and indicates to the library to release the hold of the mount relative to the request.
The drive resource provider, in an alternative embodiment, waits a predetermined time period, and, if during the predetermined time period a request for deallocation of a data storage drive and demount of any portable data storage cartridge at the deallocated data storage drive occurs, allocates the deallocated data storage drive to the reques
Basham Robert Beverley
Dahman Kirby Grant
Day III Kenneth Fairclough
Jesionowski Leonard George
Holcombe John H.
International Business Machines - Corporation
Tran Khoi H.
LandOfFree
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