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| Line 20: |
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| | * HSC40 | | * HSC40 |
| − | * HSC50 | + | * [[HSC50 Mass-Storage Controller|HSC50]] |
| | * HSC60 | | * HSC60 |
| | * HSC65 | | * HSC65 |
| Line 26: |
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| | * HSC90 | | * HSC90 |
| | * HSC95 | | * HSC95 |
| − |
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| − | == HSC50 ==
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| − | Introduction to the HSC50 in the [[VMS|VAX/VMS]] V3.3 Release Notes (1983):
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| − |
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| − | The HSC50 is a high-speed, reliable, high-availability controller of mass-storage devices.
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| − | This release supports its use in controlling [[RA60]], [[RA80]], and [[RA81]] disks, and its use with [[VAX-11/780]] and [[VAX-11/782]] systems.
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| − | The HSC50 communicates with VAX-11/780 and VAX-11/782 systems by means of the [[CI780]], which is described in the VAX/VMS CI780 Software Release Notes and the VAX/VMS Version 3.1 Release Notes.
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| − |
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| − | The HSC50 is a controller that, like the [[UDA50]], implements the [[Digital Storage Architecture]] (DSA).
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| − |
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| − | The HSC50, in implementing DSA, controls the physical disk unit.
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| − | VAX/VMS processes request virtual or logical I/O on disks controlled by the HSC50.
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| − | The disk-class driver and the HSC50 cooperate to provide what appears to the requesting process as a range of contiguous, good, logical blocks.
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| − |
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| − | The HSC50 corrects bad blocks on the disk without the intervention of VAX/VMS by revectoring the file's logical block to another, good physical block on the disk.
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| − | The VAX/VMS system, which does logical or virtual I/0 to such a disk, is never burdened by bad block correction for disks attached to an HSC50.
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| − |
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| − | With certain restrictions, the HSC50 allows two or more processors to access files on the same disk.
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| − | In addition, the HSC50 allows you to add disks to your configuration, or remove them, without rebooting your systems.
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| − |
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| − | === HSC50 Description ===
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| − | [[File:HSC50_Subsystem_Block_Diagram.png|400px|thumb|left|HSC50 Subsystem Block Diagram]]
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| − |
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| − | The HSC50 is defined as an intelligent mass storage subsystem server housed in a single cabinet.
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| − | Up to seven types of modules are contained in the HSC50.
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| − | Module names, module numbers (stamped on the module handle), and the function of each module follow:
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| − |
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| − | * Port Link Module (L0100) - Communicates over the computer interconnect (CI). This module is also known as CI Link.
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| − | * Port Buffer Module (L0109 or Pila) - Provides a limited number of high-speed buffers used to stage CI transfers.
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| − | * Port Processor Module (L0107-YA or K.pli) - Functions as the interface between the CI and the rest of the subsystem.
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| − | * Disk Data Channel (L0108-YA or K.sdi) - Supports up to four SDI disk drives (for example, the RA80, RA81, and/or RA60).
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| − | * Tape Data Channel (L0108-YB or K.sti) - Supports up to four STI tape formatters (for example, the TA78).
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| − | * Memory Module (L0106-AA or M.std) - Contains three areas of memory: control memory (128K bytes), data memory (128K bytes), and program memory (256K bytes).
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| − | * I/O Control Processor Module (L0105 or P.ioc) - Defines and directs all internal activity within the HSC50 subsystem. Contains an [[F-11]] chip set microprocessor.
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| − |
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| − | In utilizing the computer interconnect, the HSC50 interfaces one or more host computer systems via the [[SC008 Star Coupler]] (a passive, RF-transformer coupling network) to a set of mass storage devices.
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| − | If the device is a disk drive, the HSC50 communicates over the Standard Disk Interconnect (SDI) bus; if it is a tape formatter, the Standard Tape Interconnect (STI) bus is used.
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| − |
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| − | The HSC50 can support a total of six disk and/or tape data channels. Each one of these data channels accommodates four cabling bulkhead ports.
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| − | Maximum disk configuration for a single HSC50 is 24 drives.
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| − | The maximum number of tape drives in each HSC50 subsystem is found in the current HSC50 release notes.
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| − |
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| − | [[Mass Storage Control Protocol]] (MSCP) is a communication protocol used over the CI between a host system and the HSC50.
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| − | This protocol enables a single class driver to replace multiple device-specific drivers.
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| − | Separate but similar protocols exist for disk and tape communication:
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| − | * Disk MSCP frees the host from responsibility for disk I/O functions and error recovery.
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| − | * Tape MSCP includes those protocol variations necessary for tape functionality in the subsystem.
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| − |
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| − | === HSC50 Features ===
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| − | The HSC50:
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| − | * Supports disk and tape drives with· data rate bursts of up to 25 megabits per second.
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| − | * Utilizes the MSCP/TMSCP protocol allowing software standardization of all future SDI/STI device drivers.
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| − | * Connects to one port on a mass storage device leaving the other port available to a different HSC50. This feature allows increased data availability through redundancy.
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| − | * Serves multiple hosts and multiple types of hosts.
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| − | * Uses radial connection to disk drives and tape formatters permitting increased configuration flexibility.
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| − | * Interprets the disk-geometry specifics (number of heads, cylinders, tracks, and sectors) of each disk drive.
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| − | * Maps around faulty sectors by replacing them from a spare sectors pool. As a result, hosts always perceive perfect media guaranteed through several levels of redundancy.
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| − | * Reads redundant copies of the sector header to ensure correct head positioning before executing any disk drive transfer.
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| − | * Utilizes an [[Error Correction Code]] (ECC) to detect and correct up to 8 independent error bursts, each up to 10 bits in length, anywhere within the data area of a sector.
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| − | * Appends an [[Error Detection Code]] (EDC) to the data that travels to the disk. As the data is read, the HSC50 repeatedly checks the EDC to ensure data integrity.
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| − |
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| − | === HSC50 Optimizing Functions ===
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| − | The HSC50 optimizes throughput using the following functions:
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| − | * Overlapping data transfers - Utilizes a multiple data channel configuration to simultaneously perform multiple I/O transfers.
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| − | * Offloading host error handling - Saves significant host computing cycles and memory space with HSC50 performing disk and tape error functions.
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| − | * Overlapping error recovery and diagnostic operations while I/O processing - Continues to service normal I/O requests while recovering from localized errors or diagnosing localized malfunctions (as long as the required subsystem resources remain available).
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| − | * Deep buffering - Allows multisector data buffering to accommodate disk transfer speeds up to 25 megabits per second while minimizing unused disk rotations.
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| − | * Overlapping seeks - Issues parallel seeks to all drives with outstanding requests. Also issues seeks in parallel with ongoing data transfers.
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| − | * Ordering seeks - Optimizes the cylinder sequence for SEEK commands to individual drives.
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| − | * Interunit rotational position sensing (RPS) - Assigns a data transfer channel to the first drive reaching a sector designated for data transfer.
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| − | * Intraunit RPS - Splits a data transfer request into a series of smaller fragments. The first fragment that appears under the disk head is transferred.
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| − |
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| − | === HSC50 Maintainability ===
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| − | Following are the HSC50 maintainability features:
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| − | * Sensing loss of cooling air flow. If this condition reaches a dangerous level, the HSC50 stops ongoing internal processes and turns itself off to avoid damage.
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| − | * Utilizing physical and electrical isolation from other computer system devices.
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| − | * Reporting detected errors to the host error-logging facility.
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| − | * Supporting an ASCII serial line for direct communication between the auxiliary terminal and HSC50 software.
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| − | * Containing onboard loadable self diagnostics, exercisers, and utilities.
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| − | * Including front panel indicators which report fault information.
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| − | * Containing modules with LEDs to indicate operational status.
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| − | * Allowing online connection or disconnection of disk drives and/or tape formatters.
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| − | * Allowing online connection or disconnection of the CI.
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| − |
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| − | === HSC50 Base Unit and Options ===
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| − | * HSC50-AA/AB: Stand alone package - contains backplane, power supply, CI Link to Star Coupler, CI interface modules, I/O control processor, memory, and modified H9642 cross products cabinet. The base unit supports six data channels and one supplemental power supply. AA = 60 Hz/120 V, AB = 50 Hz/240 V.
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| − | * HSC5X-BA: Disk data channel - supports up to four SDI disk drives (RA80, RA81, and/or RA60).
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| − | * HSC5X-CA: Tape data channel - supports up to four STI tape formatters (TA78).
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| − | * HSC5X-EA/EB: Auxiliary power supply - adds the power supply required when more than eight modules are configured in the same base unit. EA = 60 Hz/120 V, EB = 50Hz/240 V.
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| − |
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| − | The HSC50 Base Unit cost 34,000 US$ in 1986; a Disk/Tape data channel was 9,500 US$ each.
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| | ==Further reading== | | ==Further reading== |
