Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the record
Reexamination Certificate
1998-08-05
2001-01-09
Faber, Alan T. (Department: 2753)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the record
C360S092100
Reexamination Certificate
active
06172833
ABSTRACT:
TECHNICAL FIELD
This invention relates to the retrieval of data stored on tape media, and, more particularly, to the speed of accessing and optimized retrieval of data stored in a serpentine pattern on tape media.
BACKGROUND OF THE INVENTION
Tape data storage is typically used for backup, archival, and/or sequential data processing purposes. Examples of sequential processing are batch updating of master files or data mining where queries are aggregated in one complete sequential scan of the data. The random retrieval of data from a sequentially recorded pattern has been relatively simple, moving longitudinally along the tape media in a sequential manner.
In the data processing industry, tape media is known for storing large quantities of data in parallel tracks which extend longitudinally of the tape. The most modern longitudinal tape formats for storing data on tape media, such as magnetic tape cartridges, are described as “serpentine”, and have higher track densities by having sets of tracks in both the “out” and “in” directions. For example, the IBM 3570 and IBM 3590 tape drives have 16 “out” tracks, 16 “in” tracks, and 4 “out” and “in” tracks. Access to data is accomplished by indexing the tape heads laterally of the tape media, a process that is very rapid as compared to searching the length of the tape media.
A serpentine longitudinal tape drive records data on a wrap (a track in a single direction) or a set of wraps in one direction along a length of the serpentine longitudinal tape media. Then, the tape drive shifts its recording heads laterally of the tape media a small distance and reverses the tape direction to record another wrap or set of wraps in the opposite direction along the length of the tape media. The tape drive continues these operations back and forth along the serpentine longitudinal tape media until all of blocks of data are written.
Since the physical locations of the data blocks longitudinally along the tape media are staggered back and forth along the tape and not in any sequential order, a straightforward sequential retrieval order of access to the data blocks is most likely not the optimal order of retrieval. Indeed, for data recorded on tape media in a serpentine pattern, the retrieval of blocks of data spaced relatively far apart on the tape will likely result in grossly sub-optimal performance, if the blocks of data are retrieved in sequential order with respect to the order they were written.
Various techniques and systems exist for recording data on and retrieving data from a tape media in a serpentine pattern.
The speed of initial access to the data stored in a serpentine pattern is relatively slow, however.
In tape drives for data stored in a serpentine pattern on a tape media, the tape head typically comprises both servo and data heads which are parallel and spaced apart a certain amount. A servo system in the tape drive employs the servo heads to follow servo tracks on the tape media, while the data heads read and/or write data on the data tracks. Also, when the serpentine data tape media is in a cartridge, a period of time is required for loading the tape cartridge into the drive. Once the cartridge is loaded, an additional period of time is required to thread or move the tape media so that it is in proximity to the tape head. Then, a further period of time is required for the tape drive servo arrangement to initialize the positioning of the tape media with respect to the tape head. This comprises moving the tape longitudinally while the servo arrangement adjusts the lateral positioning of the tape head so that the servo head is properly aligned with the desired servo track and the data head(s) is aligned with the corresponding data wrap (or group of wraps).
In a single reel tape cartridge the device block map is typically at the beginning of the tape. Thus, after the tape leader has been loaded by threading, and the servo head has been properly aligned, the tape data head reads the device block map and a processor processes the device block map in view of the incoming data retrieval request to optimize the retrieval order.
In a reel-to-reel tape cartridge (or cassette), the device block map is typically at the midpoint of the length of tape and the cartridge is stored with an equal amount of tape on each reel. Thus, after the tape or tape head has been moved, typically in a direction normal to the surface of the tape, into proximity to each other, and the servo head has been properly aligned, the tape data head reads the device block map and a processor processes the device block map in view of the incoming data retrieval request to optimize the retrieval order.
If the cartridge is stored in an automated tape library, such as an IBM 3575 Tape Library Dataserver, a still further amount of time is required to retrieve the cartridge from its storage slot and move the cartridge and deliver it to the tape drive.
SUMMARY OF THE INVENTION
It is an object of the present invention to increase the speed of accessing data stored in a serpentine pattern on a tape media, while achieving the optimized retrieval of such data.
Disclosed is a data storage system for use with a tape cartridge having a tape media storing data in a serpentine pattern, and having a memory device for storing a device block map for the tape media. The storage system has a memory interface for transferring data with the memory device and a tape drive for reading and/or writing data on the tape media. The tape drive, or a loading mechanism, first positions the tape cartridge at the memory interface, and subsequently positions the tape media for reading and/or writing. A processor is coupled to the memory interface and processes the device block map from the memory device for optimal retrieval of the serpentine pattern data of the tape media by the tape drive. The transfer of the device block map from the memory device and the processing of the device block map occurs while the tape drive or loading mechanism positions the tape media for reading so that the processor begins the reading process immediately upon the positioning of the tape media.
In another aspect of the invention, the tape cartridge is stored in one of a plurality of storage slots of an automated data storage library having a robotic accessor for moving the tape cartridge amongst the storage slots and at least one tape drive. In an initial step, the robotic accessor moves the tape cartridge to the tape drive. The memory interface is at the robotic accessor, and the tape cartridge is positioned at the memory interface during the move, and the stored device block map is transferred from the memory device at the memory interface to the processor, also during the move.
For a fuller understanding of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.
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Hillyer, Bruce K., et al., “Random I/O Scheduling in Online Tertiary Storage Systems”,ACM Conference, 1996, pp. 195-204.
Fry Scott Milton
Johnson Steven Douglas
Wilson Steven Bennett
Faber Alan T.
Holcombe John H.
International Business Machines - Corporation
Sullivan Robert H.
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