1. Technical Field
This invention relates to management of a data storage array. More specifically, the invention relates to a robotic arm employed with a data storage array to communicate with and control power delivery to the individual storage media in the data storage array.
2. Description of the Prior Art
Modern computer systems require large quantities of information storage. To meet this requirement computer data storage is available in many forms. A fast, but expensive and usually volatile form of data storage is main memory, typically including monolithic semiconductor circuits. Other available forms of data storage include magnetic direct access storage devices, magnetic tape storage devices, and optical recording devices. These types of data storage actually store data on electromagnetic or optical media. Each of these other types of data storage has a greater storage density and lower cost than main memory. However, these other devices require mechanical movement and therefore have slower data access times than purely electronic main memory.
Storing all system data in main memory is costly. However, storing all system data on one or more peripheral storage devices reduces performance. Thus, a typical computer system includes both main memory and one or more data storage devices arranged in a data storage hierarchy. In such a hierarchy, main memory is often referred to as the primary data storage. The next level of the hierarchy is known as secondary storage, etc. Generally, the highest level of the hierarchy has the highest performance and highest cost. Often at the lowest level of the hierarchy, the media is referred to as being removable, examples of which are tape and optical cartridges. By transferring data between different levels of the hierarchy, as required, cost and performance may be optimized.
In order to have the information available on an “as needed” basis, much storage at the lowest level of the hierarchy is required. Business applications typically use numerous portable data storage media including floppy disks, optical disks, or magnetic tapes, to meet the required data storage needs. Prior art data storage libraries have been developed to manage the storage of such portable disks or tapes. Some storage libraries employ automatic means including robotic picker and gripper devices to store and access such portable data storage media. Others do not employ automatic means, but rather rely on human operators to store and access conventional portable data storage media when needed.
Prior art data storage libraries include a plurality of storage bins or slots for retaining portable data storage media, such as magnetic tapes, magnetic disks, or optical disks. Each portable data storage medium may be contained in a cassette or cartridge housing for protection. In this regard, a drive unit having a portable data storage medium mounted therein and allocated for use is referred to as “unavailable.” Conversely, a drive unit without a portable data storage medium mounted therein, or unallocated, is referred to as “available.” Once a portable data storage medium is mounted in a drive unit, and the medium is allocated for use, data may be written to or read from that medium for as long as the system requires. Data is stored on a medium in the form of one or more files, with each file being a logical data set.
However, as noted above, there are limitations in the prior art configurations of data storage libraries. For example there may be a human factor that affects the efficiency of operation associated with storage of data on storage media located in the library. Therefore, there is a need to configure a storage library that mitigates or eliminates the degradation of performance associated therewith.
While many library configurations are possible, the storage media in a library is generally either static or picked. Static media remains in place and is accessed electrically, for example through a system of power lines and data cables which in turn may be operated in conjunction with relays and which are an integral part of the library infrastructure. This method of accessing is very costly and complex due to the large amount of wiring and electronics and due to the connectivity issues that arise in maintaining the networked status of the media blocks. Picked media is accessed robotically, removed from a slot and transported to a drive unit which then reads from or writes to the medium. This configuration has the disadvantages of slow data access and limited overall throughput due to the limited number of drives available for reading from and writing to the media.
Therefore, there is also a need to configure a storage library such that the media is neither picked nor permanently wired into an existing infrastructure.