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BACKGROUND OF THE INVENTION
This invention relates generally to data storage and retrieval, and more
particularly to an improved method and apparatus for storing and
retrieving large amounts of data contained in magnetic tape cartridges.
There exists a need in the marketplace, since the advent of computers such
as the IBM 360/370, to store large amounts of data (e.g., in excess of 1
trillion bits) while consuming as little floor space as possible, and at
the same time making the data readily available. Basically, two choices
for data storage have existed: (1) online, usually direct access storage
devices (DASD), which provides fast initial service time through
sequential or direct processing; or (2) offline, usually manual 9-or
18-track magnetic tapes, which provides a low unit cost per unit storage.
There exists a need, however, for many new applications were costly DASD
are not justified but where manual tape systems are considered too slow or
too inconsistent.
One early approach, used in the IBM 3850 Mass Storage System, consists of
an array of data cartridges about 1.9 inches in diameter and 3.5 inches
long, with a capacity of 50 million characters each. Each cartridge
contains magnetic tape 2.7 inches wide and 64 feet long, on which data is
organized in cylinders analogous to those of a disk file and can be
transferred to the disk file one cylinder at a time. Up to 4700 cartridges
can be stored in hexagonal compartments in a honeycomb-like apparatus that
includes mechanisms for fetching cartridges from the compartments, for the
reading and writing of data on them, and for the replacement of cartridges
in the compartments. The fetching and replacing mechanism, however, is
adapted to store and retrieve the cartridges from a linear rack.
Accordingly, if a desired cartridge is located remotely from the
retrieving mechanism at one end of the rack, the retrieving mechanism
would be required to move to the end, retrieve the cartridge, and load it
upon a drive. It is, therefore, apparent that if a subsequently selected
cartridge is located at the other end of the rack, much wasted time would
be utilized in the movement of the retriever mechanism between opposite
ends of the rack.
Various other tape library systems, have been devised for the storage and
handling of magnetic tape reels. More sophisticated systems which have
been used in the past, commonly referred to as automated tape library
systems, permit storage and automatic retrieval of data contained on tape
reels such as the conventional IBM 3420 tape subsystems. As is well known,
such tape subsystems provide a nominal data rate of 1.25 megabytes per
second, a recording density of 6250 bytes per inch, and a storage capacity
of 165 megabytes on 9-track, 1/2 inch iron oxide magnetic tape wound about
101/2 inch reels. The tape reels, with tape supported by conventional
vacuum columns, are loaded upon a drive system including a laminated
magnetic head.
One prior art automated tape library system utilized for storing and
retrieving data contained on such tape reels is disclosed in U.S. Pat. No.
3,920,195. The apparatus taught therein corresponds generally to the Xytex
Corporation XTL tape library which, under the control of an IBM operating
system, automatically brings tapes from storage positions on either side
of a linear rack, mounts them on tape drives, dismounts them when the job
is completed, and returns each reel to storage. Average access time for
delivery of a single tape reel to a selected drive in a medium size system
(accommodating up to 2.3 trillion bits of storage in 3200 magnetic tape
reels), however, is relatively slow. Such access times include
selector-positioning mechanism access, reel selection, access to the
automatic mounting unit, and the mounting of the reel on the tape drive
(i.e., elapsed time from the operating system command to mount a tape to
the time that the tape is physically mounted and ready to start the tape
drive load cycle).
All reel storage matrices within the linear racks are serviced by the reel
selector-positioning mechanism, which is part of the library control unit
but which moves through each library storage unit on a connecting rail.
The selector-positioning mechanism selects and replaces reels from the
library storage units through use of a segment which rotates 180.degree.
for the selection and replacement of reels on each side of the linear
library storage unit.
When a reel mount command is received by the library control unit, the
selector-positioning mechanism is commanded to move to the address of the
required reel in the array. After the selector-positioning mechanism
reaches the addressed position, the reel is drawn from its storage
location and the selector-positioning mechanism is then moved to the
automatic reel mounting unit which will service the particular tape drive
that the system indicates. When the selector-positioning mechanism reaches
that location the reel is deposited in a pre-load position. The automatic
reel mounting unit then transports the reel to the tape drive and mounts
it.
The automatic reel mounting unit retracts within the storage unit when not
in use. There is a protective hood enclosing the drive hub of the tape
drive which provides safety and security, and which can be pivoted out of
the way by an operator to facilitate cleaning and servicing. Pivoting the
hood automatically removes the drive from control of the system and makes
it accessible for manual loading.
One particular drawback to the aforedescribed automatic tape library
system, however, resides in its linear storage configuration. Like the IBM
3850 Mass Storage System, the system described in U.S. Pat. No. 3,920,195
suffers from certain access inefficiencies in cases where a selected tape
reel is located at one end of the library, while the next selected tape
reel is stored at the other end. Moreover, while the storage density per
unit area of floor space taken up by the system is doubled through use of
a two-sided linear rack, large storage systems incorporating more than one
library storage unit merely aggravate the problems of linear storage by
extending the path through which the selector-positioning mechanism must
go to transit from one end of the library to the other.
Nevertheless, the use of standardized magnetic tape reels has been more
recently supplanted by small, rectangular cartridges such as those which
are used in the IBM 3480 tape subsystem. The rate at which data can be
stored in the cartridge's one-half-inch wide chromium dioxide tape, or
retrieved from it, is the result of using 18 recording tracks and
achieving a linear data recording density of about 38 thousand bytes per
inch (approximately six times the density used in typical tape reel
drives). Moreover, the four-by-five inch cartridge used in the IBM 3480
tape subsystem is about one-fourth the size of a standard 10.5-inch reel
of magnetic tape, yet it stores up to 20% more data, a total of 200
million characters. The tape and cartridge requirements for the system are
as defined in the IBM document "Tape and Cartridge Requirements for the
IBM 3480 Magnetic Tape Drives", GA 32-0048-0, the contents of which are
incorporated herein by reference. Further details are disclosed in U.S.
Pat. No. 4,426,047 and U.S. Pat. No. 4,383,660, and in the "Second Draft,
Proposed American National Standard, Unrecorded, Magnetic Tape and
Cartridge for Information Interchange" (ANSI-X 3 B 5/85-030, Feb. 1985),
each of which is incorporated herein by reference.
While the advances provided by the digital servo control and new head
technology of the IBM 3480 Magnetic Tape Subsystem permit low acceleration
tape motion thereby eliminating the need for vacuum columns, capstans, and
reflective markers have improved the level of data reliability as compared
to conventional drives, the advantages gained are nearly offset by the
disadvantages accruing from the use of book shelf type storage racks such
as those described in U.S. Pat. No. 4,600,107. Furthermore, while the
now-standardized IBM 3480 magnetic tape cartridges improve such data
reliability through reduction of both contaminants and handling damage,
the storage and retrieval of such cartridges must for the most part be
carried out by human operators. Such human intervention not only degrades
the reliability of selection and replacement, but also prolongs the time
from which a data request is made and that data is read by loading a
specific cartridge in an available tape drive. While recent improvements
to systems utilizing the IBM 3480 cartridge which incorporate magazine
type automatic loaders have reduced the time that jobs wait for cartridges
to be mounted, such systems still require operator assistance and are
inflexible as to the mounting order once installed within the magazine. It
would, therefore, be desirable to provide a storage and retrieval system
for magnetic tape cartridges such as those of the IBM 3480 type which are
capable of storing large amounts of data, while consuming as little floor
space as possible, and at the same time making the data readily available
by minimizing human intervention.
Two such approaches used in the past are disclosed and claimed in U.S. Pat.
No. 3,938,190 and U.S. Pat. No. 4,527,262. Unlike each of the above
described storage and retrieval systems, the systems shown in U.S. Pat.
No. 3,938,190 and U.S. Pat. No. 4,527,262 are both adapted for storing
information-bearing units or modules in a polygonal configuration. For
example, the storage and retrieval system for magnetic tape cassettes
described in U.S. Pat. No. 3,938,190 includes a fixed two-dimensional
storage array, a fixed processing or play station for extracting
information from the units, and a movable selection mechanism having three
degrees of freedom for retrieving individual modules from the storage
area, transferring them to the processing area, and then returning them to
the storage area after the information contained therein has been
extracted. Additionally, the system includes means for automatically
sequencing a series of units, as well as a preprocessing station for cuing
up individual units for intra-unit accessing.
The information storer and retriever shown in U.S. Pat. No. 4,527,262, on
the other hand, includes a plurality of shelves disposed so as to be
substantially tangent to a cylinder of reference of a given diameter
defining an access corridor which is large enough to accommodate a
transport apparatus in the approximate center of the corridor. The
transport mechanism includes a carriage that is translatably disposed on a
pair of parallel rods to effect X-axis translation of the carriage through
the access corridor of the polygonal arrangement, and means for rotating
the transport mechanism about the X-axis to select a particular shelf
disposed within the polygonal arrangement. Once the appropriate angular
position is achieved and the carriage has been translated in the
appropriate distance along the X-axis, then the in and out movement or
X-axis translation is ready for activation by appropriate means.
Each of the aforedescribed U.S. Pat. Nos. 3,938,190 and 4,527,262
effectively stores and retrieves a plurality of information bearing media,
but both are limited in the amounts of discrete media which may be
contained therein. The substantially circular arrays provided increase the
amounts of data which may be stored per unit floor space, but neither
system includes the capability for expansion of storage by interconnecting
individual storage units, one with the other, to improve data handling
efficiency.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide an
improved method and apparatus for storing and retrieving large amounts of
information. More specifically, it is an object of the present invention
to provide a storage and retrieval subsystem in a data processing system
having a host computer and a plurality of tape transports coupled for
communication with the host computer, each of the tape transports being
adapted for use with magnetic tape cartridges.
Another object of the present invention is to provide an automated
cartridge system for storage and retrieval of magnetic tape cartridges
used in a data processing system, thereby minimizing the requirements for
human intervention.
Still another object of the present invention is to provide an automated
cartridge system which stores the cartridges in a first position adapted
to prevent damage to the magnetic tape contained therein, and which
transfers selected cartridges from their stored position to a second,
transducing position upon the tape transports for reading data therefrom
or writing data thereto.
Yet another object of the present invention is to provide an automated
cartridge system which is capable of communicating with a plurality of
host computers.
A further object of the present invention is to provide an automated
cartridge system which includes improved robotic means having a plurality
of degrees of freedom for rapidly accessing a selected magnetic tape
cartridge and loading it within a particular tape transport.
Still a further object of the present invention is to provide an improved
robotic means with redundant means for picking and placing individual
magnetic tape cartridges.
Yet a further object of the present invention is to provide an automated
cartridge system which is accessible for manual loading of magnetic tape
cartridges, as well as the transference of a plurality of magnetic tape
cartridges between discrete storage modules.
Another object of the present invention is to provide a method of
controlling the storage and retrieval of data which optimizes the robotics
motion to maximize media handling performance.
Still another object of the present invention is to provide a method of
controlling the storage and retrieval of data from magnetic tape
cartridges which is capable of interfacing a plurality of host computers
with a plurality of storage modules.
Yet another object of the present invention is to provide an automated
cartridge system which includes means for self-calibration and
self-diagnosis.
A further object of the present invention is to provide a storage cell for
containing a magnetic tape cartridge in an automated cartridge system, the
storage cell including a unique target which minimizes fine adjustments to
the robotic means when used in conjunction with a conventional vision
system.
Briefly, these and other objects of the present invention are accomplished
by a storage and retrieval subsystem in a data processing system, wherein
the subsystem includes a plurality of magnetic tape cartridges, a host
computer, and library means for storing the plurality of magnetic tape
cartridges in substantially upright positions. The library means according
to the invention includes a first cylindrical array of storage cells
centered about a vertical axis, a second cylindrical array concentrically
arranged about the first array, and a library tape unit including a
plurality of tape drives, each of the tape drives being adapted to receive
one of the magnetic tape cartridges in a substantially horizontal
transducing position. Robotic means within the library means is used to
transfer selected ones of the magnetic tape cartridges between their
substantially upright positions and the substantially horizontal
transducing positions at a selected tape drive. First controller means
outboard a channel communicating with the host computer is adapted to
receive commands from the host computer for interfacing between the host
computer and the library means, and second controller means inboard of the
channel is adapted to receive commands from the outboard controller means
for interfacing between the outboard controller means and the robotic
means.
In accordance with one important aspect of the invention, the robotic means
includes a six-motion, servo controlled mechanism for picking a magnetic
tape cartridge selected by the host computer, transferring that cartridge
to an available tape drive, and loading the cartridge upon the tape drive
in a transducing position for writing data thereto or reading data
therefrom.
In accordance with another important aspect of the invention, the library
means may comprise a plurality of storage modules, each comprising first
and second cylindrical arrays, wherein the individual storage modules are
connected for transference of magnetic tape cartridges therebetween in
order to modularize the library means and thereby provide the capability
for add-on storage. The transference means, according to the present
invention, includes means for accepting cartridges placed by the robotic
means of one storage module in order that they may be picked by the
robotic means of another interconnected storage module.
In accordance with still another important aspect of the invention, each
storage module includes means for inputting and outputting cartridges by
manual means, while maintaining the automated capability of the robotic
means. Such input/output means further comprises safety means for
preventing access to the interior portion of the storage module while the
robotic means are in operation.
Other objects, advantages, and novel features of the present invention will
become more apparent from the following detailed description of a
preferred embodiment when considered in conjunction with the accompanying
drawings wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates an automated cartridge system according to one
embodiment of the present invention;
FIG. 2 is a block diagram of an expanded ACS according to the present
invention;
FIG. 3 illustrates in plan view, partially cut away, a library storage
module with its associated tape drives and library control unit;
FIG. 4 illustrates in elevational view the library storage module and
associated tape units of FIG. 3 taken along the lines IV--IV;
FIG. 5 is a sectional view of the harmonic drive means shown in FIG. 4
taken along the lines V--V, and a view partially cut away of a crash stop
according to the present invention;
FIG. 6 illustrates the Z-mechanism and wrist assembly shown in FIG. 4 taken
along the lines VI--VI;
FIG. 7 illustrates in plan view the Z-mechanism and wrist assembly shown in
FIG. 6 taken along the lines VII--VII;
FIG. 8 illustrates in sectional view one hand and finger assembly and roll
mechanism of the wrist assembly shown in FIG. 7 taken along the lines
VIII--VIII;
FIG. 9 illustrates the hand and finger assembly of FIG. 8 at its extended
position;
FIG. 10 illustrates in sectional view the finger assembly of FIG. 8 taken
along the lines X--X;
FIG. 11 illustrates in front elevational view the hand and finger assembly
of FIG. 8 taken along the lines XI--XI;
FIG. 12 illustrates the hand and finger assembly of FIG. 11 rotated
90.degree. for storage of the magnetic tape cartridge;
FIG. 13 illustrates in plan view a carriage for loading the magnetic tape
cartridge in conjunction with the hand and finger assembly shown in FIG.
8;
FIG. 14 illustrates the carriage assembly of FIG. 13 in its unloaded
position;
FIG. 15 illustrates the carriage of FIG. 13 in its loaded position;
FIG. 16 is a block diagram of the tape transport shown in FIG. 4, as well
as its associated tape control unit;
FIG. 17 illustrates in plan view the access doors and cartridge access port
shown in FIG. 3;
FIG. 18 illustrates an elevation view, partially cut away, the cartridge
access port shown in FIG. 3 taken along the lines XVIII--XVIII;
FIG. 19 illustrates in sectional view the cartridge access port of FIG. 18
taken along the lines XIX--XIX;
FIG. 20 illustrates the cartridge access port of FIG. 19 in its opened
position;
FIG. 21a illustrates in detail the pass through port shown in FIG. 3;
FIG. 21b illustrates another embodiment of the pass through port;
FIG. 21c illustrates in sectional view the pass through port shown in FIG.
21b;
FIG. 22 illustrates a storage cell for containing magnetic tape cartridges
in accordance with the present invention.
FIG. 23 is a block diagram of a library management unit (LMU) according to
the present invention;
FIG. 24 illustrates passage of data within a central processor module (CPM)
of the LMU shown in FIG. 23;
FIGS. 25a and 25b illustrate paged memory mapping of the CPM shown in FIG.
24;
FIGS. 26a and 26b illustrate various external registers of the CPM shown in
FIG. 24;
FIG. 27 is a block diagram of an interface processor according to the
present invention;
FIG. 28 shows external registers used with the interface processor of FIG.
27;
FIG. 29 illustrates interrupts used with the interface processor of FIG.
27;
FIG. 30a-30f illustrate details of the external registers shown in FIG. 27;
FIG. 31 shows a block diagram of a serial time interrupt controller
according to the present invention;
FIG. 32 illustrates an IPM interface according to the present invention;
FIG. 33 shows an LMU operator's panel;
FIG. 34 illustrates transfer of data from a terminal control unit to the
LMU;
FIG. 35 illustrates further transfer of data between the terminal control
unit and LMU;
FIGS. 36a-36d show MOUNT requests and responses with a flow chart of ACS
actions;
FIGS. 37a and 37b show DISMOUNT requests and responses;
FIGS. 38a-38c show SWAP requests and responses with a flow chart of ACS
actions; FIGS. 39a-39c show MOVE requests and responses with a flow chart
of ACS actions;
FIG. 40 shows a flow chart of ACS actions upon an ENTER command;
FIGS. 41a and 41b show CATALOG requests and responses;
FIG. 42 illustrates transmission and acknowledgment of an LMU
communication;
FIGS. 43a-43e illustrate commands, responses, rejects and error messages
between the LMU and an LSM;
FIGS. 44a and 44b illustrate commands responses, rejects and error messages
associated with the cartridge access port;
FIG. 45 illustrates commands, responses, rejects, and error messages
associated with the pass through port;
FIG. 46 illustrates LSM monitoring communications;
FIG. 47 describes control program interfaces to LMU tasks and hardware;
FIG. 48 shows input/output through LMU software;
FIG. 49 is a block diagram of LMU functional software;
FIG. 50 illustrates an exemplary process host request task;
FIG. 51 lists system calls used by the control program;
FIG. 52 shows a block diagram of LSM functional software architecture; and
FIG. 53a-53c are block diagrams of LSM data flow.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings, wherein like characters designate like or
corresponding parts throughout the several views, there is shown in FIG. 1
an automated cartridge system (ACS) 100 according to one embodiment of the
present invention. The ACS 100 is designed to operate with an IBM, or
IBM-compatible host computer 102 capable of communication with a
conventional 327X-type terminal controller 104 as will be described in
further detail herein below. Comprised generally of a library management
unit (LMU) 106 and a library storage module (LSM) 108, the ACS 100,
through its associated host software component (HSC) 110, enables storage
and retrieval of approximately 6000 magnetic tape cartridges of the IBM
3480-type for use by the host computer 102 across a conventional channel
112. Each LMU 106 serves as the library controller and provides the
interface between from one to sixteen host computers 102 and up to 16 LSMs
108, as shown in FIG. 2. The LMU 106 thus acts as an outboard controller
and interprets commands from the host computers 102, relaying appropriate
instructions to the selected LSM 108 via a control path (shown in solid
lines) and a library control unit (LCU) 109. On the other hand, the
read/write data path (dashed lines) comes directly from the host computer
102, through a tape control unit 111 to the tape transports 150 as will be
described further herein below, thereby separating control signals from
data signals.
Each LSM 108 provides the necessary mechanisms for automated cartridge
handling. It not only provides the storage area for magnetic tape
cartridges utilized in the system, but also includes an optical system for
identifying the correct cartridge, a servo-controlled, electromechanical
means of selecting the proper cartridge and delivering it to the correct
tape drive, and a suitable housing to ensure operator safety and data
security. As shown in greater detail in FIG. 3, a LSM 108 is comprised
generally of an outer housing 113 which includes a plurality of wall
segments 114 attached to floor plates 116 and disposed about a vertical
axis A. An inner wall 118 having a plurality of segments 120 forming an
upper portion 122 which is suspended from a ceiling 124 of the LSM 108,
and another plurality of segments 126 forming a lower portion 128 which is
mounted upon the floor plates 116, supports a first cylindrical array 130
of storage cells 132 centered about the vertical axis A. A second
cylindrical array 134 of storage cells 132 is concentrically arranged
about the first array 130, mounted upon the wall segments 114 of the outer
housing 113.
Because conventional magnetic tape cartridges of the IBM 3480-type are
subjected to an uneven tension upon rewinding of the tape contained
therein, portions of the tape may project away from the wound body thereby
facilitating damage to such portions if stored in a position which would
cause undue pressure and potential bending or breakage of those portions
projecting from the wrapped body. It would, therefore, be desirable to
store such magnetic tape cartridges in a substantially upright position to
alleviate such problems. The use of the term "upright", it should be
apparent, indicates a position in which the axis of the tape reel hub
within the cartridge is in a substantially horizontal position rotated
approximately 90.degree. from its transducing position.
As shown in FIG. 4, when viewed in conjunction with FIG. 3, it can be seen
that an access path 136 is formed between the upper and lower portions 122
and 128 in order that an arm assembly portion 138 of robotic means 140 may
rotate about the vertical axis A between the first and second cylindrical
arrays 130 and 134. The arm assembly portion 138 includes a theta arm 142
rotatably mounted upon a support column 134 which is attached to the floor
plates 116. The arm assembly portion 138 further includes a Z-mechanism
146 attached to the end of the theta arm 142 remote from the support
column 144. A wrist assembly 148, coupled to the Z-mechanism 146, is thus
provided up-and-down motion as indicated by the arrows in FIG. 3 for
storage and retrieval of magnetic tape cartridges contained within the
storage cells 132, and for loading and unloading of the tape cartridges
within a selected tape transport 150 of a tape unit 152 attached to the
side of the LSM 108. Each LSM 108, as will be described in further detail
herein below, is capable of supporting up to sixteen tape transports 150,
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