Direct access storage device with independently stored parity

• US 5,072,378 A
• Filed: 12/18/1989
• Issued: 12/10/1991
• Est. Priority Date: 12/18/1989
• Status: Expired due to Term

• Current Assignee: Storage Technologies Corporation (Oracle Corporation)
• Original Assignee: Storage Technologies Corporation (Oracle Corporation)
• Inventors: Manka, Paul S.
• Primary Examiner(s): Bowler, Alyssa H.
• Application Number:
  US07/452,674
• Time in Patent Office: 722 Days
• Field of Search: 364/200 MS File, 364/900 MS File, 365/200, 365/230.03, 365/230.04, 360/22, 360/24, 360/27, 371/2.2, 371/39.1, 371/37.7, 371/38, 371/40.1, 371/40.4
• US Class Current: 714/6.12
• CPC Class Codes: G06F 11/1008 in individual solid state devices G06F11/1004 takes precedence
• CPC Class Codes: G06F 11/1076 Parity data used in redundant arrays of independent storages, e.g. in RAID systems
• CPC Class Codes: G06F 3/0601 Interfaces specially adapted for storage systems
• CPC Class Codes: G06F 3/0673 Single storage device
• CPC Class Codes: G11B 19/28 Speed controlling, regulating, or indicating G11B19/24 takes precedence
• CPC Class Codes: G11B 20/1252 for discontinuous data, e.g. digital information signals, computer programme data
• CPC Class Codes: H03M 13/27 using interleaving techniques

Abstract

A failure independent, fault tolerant Direct Access Storage Device (DASD) storage subsystem comprising a Disk Control Unit and a number of Physical Devices is provided with a parity Generator for generating a parity for system records as the system records are transferred between the storage subsystem and a CPU of a data processing system. The parity is stored on a different unit so that if one unit containing portions of a system record becomes unavailable, the unavailable portion of the record is reconstructed during transfer to the CPU from the remainder of the record and the parity. The storage system of the invention can accommodate variable length data records without requiring operating system modifications.

Claims

1. A method of operating a logical data storage system connected to a computer via a data channel for an exchange of data between said computer and said logical data storage system, said logical data storage system comprising a parity storage unit and n sequentially arranged data storage units comprising a logical storage unit, said method comprising the steps of;

applying segments of virtual data records of different virtual tracks from said computer via said channel to said logical data storage system,

sequentially distributing applied segments of a virtual record to said n data storage units so that each applied segment is distributed to a single unit and so that all of said n data storage units together receive segments comprising the entirety of said virtual record,

generating a parity segment representing the parity of each group of n applied segments in response to the distribution of said each group of n segments of said virtual record to said n data storage units,

distributing each generated parity segment to said parity storage unit, and

interleaving distributed segments of different virtual tracks onto a single logical track of said logical unit by writing each distributed segment into the storage unit to which said segment is distributed so that segments of virtual records of a first virtual track are written into alternate and non adjacent logical sectors of a single logical track and so that the logical sectors of said single logical track not containing segments of said first virtual track are written to contain segments of another virtual track.

2. The method of claim 1 in which each of said virtual records comprises a plurality of fields separated by gaps and wherein each of said logical sectors serves the dual function of storing segments of a virtual record of one virtual track while simulating a gap of a virtual record of another virtual track.

3. The method of claim 2 wherein each of said virtual tracks are on the same virtual cylinder.

4. The method of claim 3 wherein said logical unit emulates the physical characteristics of a virtual device containing said virtual records.

5. A method of operating a logical data storage system connected to a computer via a data channel for the exchange of data between said computer and said logical data storage system, said logical data storage system comprising n sequentially arranged data storage units forming a logical storage unit and a parity storage unit, said method comprising the steps of;

operating said logical data storage system for receiving bytes of virtual data records of at least two different virtual tracks from said computer via said channel, each of said records having a plurality of fields separated by gaps,

sequentially distributing received bytes of each virtual record to said sequentially arranged n data storage units so that each received byte is distributed to a single unit and so that all of said n data storage units together receive bytes comprising the entirety of said each virtual record,

generating a parity byte representing the parity of each group of n received bytes of a virtual record in response to the distribution of said each group of n bytes to said n data storage units,

distributing each generated parity byte to said parity unit concurrently with the distribution of the last byte of the group of n bytes from which said parity byte is generated, and

interleaving received bytes of different virtual tracks onto a single logical track of said logical data storage unit by writing each distributed byte into the unit to which said byte is distributed so that the bytes of virtual records of a first virtual track are written into a plurality of alternate and nonadjacent logical sectors of a single logical track comprising a corresponding track of each of said n units, said writing being effected in such a manner so that adjacent sectors of said logical track contain bytes of virtual records from different virtual tracks and so that each logical sector serves the dual function of storing data bytes of a virtual record of one virtual track and for simulating a gap for another virtual record of another virtual track.

6. A method of operating a logical data storage system adapted to emulate a virtual data storage system, said logical data storage system comprising a logical disk storage unit connected to a computer via a data channel for the exchange of data between said computer and said logical data storage system, said method comprising the steps of;

operating said logical system for receiving bytes of virtual records of different virtual tracks from said computer via said channel,

applying received bytes of each virtual record to said logical disk unit,

interleaving received bytes of different virtual tracks onto a single logical track of said logical unit by writing received bytes representing a first virtual record of a first virtual track into a plurality of alternate and nonadjacent logical sectors of a single logical track of said logical disk unit, and

writing received bytes representing another virtual record of another virtual track into the logical sectors of said logical track that do not contain bytes of said first logical record and that are intermediate and adjacent the logical sectors of said logical track that do contain bytes of said first virtual record,

said writing being effected in said interleaved manner so that adjacent sectors of said logical track contain bytes of different virtual records from said different virtual tracks.

7. The method of claim 6 wherein said different virtual tracks are on the same virtual cylinder of a virtual disk unit containing said virtual tracks.

8. The method of claim 6 wherein;

said logical disk unit comprises n different data storage disk units spindle synchronized so as to maintain rotational synchronization,

said step of applying comprises the step of sequentially distributing the received bytes of each virtual record to said n units so that each received byte is distributed to a single unit and so that all of said n units together receive the bytes comprising the entirety of each received virtual record, and

said step of writing comprises the step of writing each distributed byte into the unit to which said byte is distributed.

9. The method of claim 8 in which said method further comprises;

the step of responding to each distribution of a byte to each of said n units for generating a parity byte for said bytes received by each of said n units, and

writing said parity byte into a parity unit.

10. The method of claim 6 wherein each of said virtual records comprises a plurality of fields adjacent to each other on the virtual track containing said each record with each of said fields of a virtual record being separated from an adjacent field by a gap characterized by a plurality of byte times, and

wherein each of said virtual records is written into alternate sectors of said logical track so that the byte times comprising said gaps for a first one of said virtual records of a first virtual track are simulated by logical sectors of said logical track that do not contain bytes of the virtual track containing said first virtual record but that do contain bytes of another virtual record of another virtual track.

11. The method of claim 10 wherein at least one field of each virtual record comprises a data field whose length is dependant upon the quantity of bytes in said data field so that the length of the data field of a first virtual record can differ from the length of the data field of another virtual record, and wherein said method further comprises the step of;

writing bytes of the data field of a virtual record into said logical sectors of a logical record with the number of logical sectors required for the writing of said data bytes being determined by the quantity of bytes in said virtual data field.

12. A method of operating a logical data storage system adapted to emulate a virtual data storage system, said logical data storage system comprising a logical disk storage unit connected to a computer via a data channel for the exchange of data between said computer and said logical data storage system, said method comprising the steps of:

operating said logical system for receiving bytes of virtual records of different virtual tracks from said computer via said channel,

applying received bytes of each virtual record to said logical disk unit,

interleaving received bytes of different virtual tracks onto a single logical track of said logical unit by writing received bytes representing a first virtual record of a first virtual track into a plurality of alternate and nonadjacent logical sectors of a single logical track of said logical disk unit, and

writing received bytes representing another virtual record of another virtual track into the logical sectors of said logical track that do not contain bytes of said first logical record and that are intermediate and adjacent the logical sectors of said logical track that do contain bytes of said first virtual record,

said writing being effected in such a manner so that adjacent sectors of said logical track contain bytes of different virtual records from said different virtual tracks;

said virtual records being recorded on said logical track in such a manner that;

a first sector on said logical track contains information for a first gap of a first virtual record of a first virtual track and a first gap of a second virtual record of a second virtual track,

a second sector adjacent to said first sector on said logical track contains home address information of both said first and second virtual records,

a third sector adjacent to said second sector on said logical track contains a count field of said first virtual record of said first virtual track,

a fourth sector adjacent to said third sector on said logical track contains a count field of said second virtual record of said second virtual track,

subsequent sectors of said logical track contain other fields of virtual records including said first and second virtual records of said first and second virtual tracks so that said other fields of said first and second virtual records are interleaved on said logical track with adjacent fields of said logical track containing bytes of virtual records of different virtual tracks.

13. A method of operating a logical data storage system adapted to emulate a virtual data storage system, said logical data storage system comprising a logical disk unit connected to a computer via a data channel for the exchange of data between said computer and said logical data storage system, said method comprising the steps of;

operating said logical data storage system for receiving segments of virtual records of different virtual tracks from said computer via said channel with said records having a plurality of fields separated by gaps,

applying received segments of each virtual record to said logical disk unit, and

interleaving received segments of different virtual tracks onto a single logical track of said logical disk unit by writing said received segments representing said virtual records into different logical sectors of a single logical track of said logical disk unit so that each logical sector serves the dual function of storing segments of a virtual record of one of said virtual tracks as well of simulating a gap time for a virtual record of another virtual track.

14. The method of claim 13 wherein said writing is effected in such a manner that received segments representing a first virtual record of a first virtual track are written into a plurality of alternate and nonadjacent logical sectors of said single logical track of said logical disk unit and so that segments representing another virtual record of a different virtual track are written into the logical sectors of said logical track not containing segments of said first virtual record,

said writing being further effected in such a manner so that adjacent sectors of said logical track contain segments of different virtual records from said different virtual tracks.

15. The method of claim 14 wherein said different virtual tracks are on the same virtual cylinder of a virtual disk unit containing said virtual tracks.

16. The method of claim 14 wherein;

said logical disk unit comprises n different data storage disk units spindle synchronized so as to maintain rotational synchronization,

said step of applying comprises the step of sequentially distributing received segments of each virtual record to said n units so that each received segment is distributed to a single unit and so that all of said n units together receive the segments comprising the entirety of each received virtual record, and

said step of writing comprises the step of writing each received segment into the unit to which said segment is distributed.

17. The method of claim 13 wherein each of said virtual records comprises a plurality of fields adjacent to each other on the virtual track containing said each record with each of said fields being separated from an adjacent field by a gap characterized by a plurality of segment times, and

wherein each of said virtual records is written into alternate logical sectors of said logical track so that segment times representing said gaps for a first one of said virtual records are simulated by sectors of said logical track that do not contain segments of said first virtual record.

18. The method of claim 13 wherein at least one field of each virtual record comprises a data field whose length is dependant upon the quantity of data segments in said field so that the length of the data field of a first virtual record can differ from the length of the data field another virtual record, and wherein said method further comprises the step of;

writing segments of a data field of a virtual record into sectors of a logical record with the number of logical sectors required for said writing of said data segments being determined by the quantity of segments in said virtual data field.

19. A method of operating a logical data storage system adapted to emulate a virtual data storage system, said logical data storage system comprising a logical disk unit connected to a computer via a data channel for the exchange of data between said computer and said logical data storage system, said method comprising the steps of;

operating said logical system for receiving bytes of virtual records of different virtual tracks from said computer via said channel with said records having a plurality of fields separated by gaps,

applying received bytes of each virtual record to said logical disk unit, and

interleaving received bytes of different virtual tracks onto a single logical track of said logical unit by writing said received bytes representing said virtual records into different logical sectors of a single logical track of said logical disk unit so that each logical sector serves the dual function of storing bytes of a virtual record of one of said virtual tracks as well of simulating a gap time for a virtual record of another virtual track;

said virtual records being recorded on said logical track in such a manner that;

a first sector on said logical track contains information for a first gap of a first virtual record of a first virtual track and a first gap of a second virtual record of a second virtual track,

a second sector adjacent to said first sector on said logical track contains home address information of both said first and second virtual records,

a third sector adjacent to said second sector on said logical track contains a field of said first virtual record of said first virtual track,

a fourth sector adjacent to said third sector on said logical track contains a field of said second virtual record of said second virtual track,

alternate subsequent and nonadjacent sectors of said logical track contain other fields of virtual records including said first and second virtual records of said first and second virtual tracks so that the fields of said first and second virtual records are interleaved on said logical track with adjacent fields of said logical track containing bytes of virtual records of different virtual tracks.

20. A method of operating a logical data storage system adapted to emulate a virtual data storage system, said logical data storage system comprising a logical disk storage unit connected to a computer via a data channel for the exchange of data between said computer and said logical data storage system, said method comprising the steps of;

assigning pairs of virtual tracks of virtual cylinders of said virtual system to a single logical track of a logical cylinder of said logical disk unit for the storage by said logical unit of bytes of virtual records on said virtual tracks, each of said pairs of virtual tracks being on the same virtual cylinder and each pair of virtual tracks being assigned to a different one of said logical tracks,

applying commands from said computer to said logical unit specifying the virtual cylinder and head and record number of a first virtual record for which updated data bytes are to be written into an assigned logical track of said logical disk unit,

operating said logical disk unit in response to the receipt of said commands specifying said virtual cylinder and head and record number for said first virtual record for which said updated data bytes are to be written to identify the area of said logical track containing said first virtual record,

sending a command from logical disk unit to said computer when said logical disk unit is in an operational position corresponding to said first virtual record on said logical track,

applying updated bytes of said first virtual record from said computer via said channel to said logical disk unit,

writing said applied updated bytes of said first virtual record into the location of said identified logical track containing said first virtual record,

said writing being effected in an interleaved manner so that said updated bytes of said first virtual record are written into a plurality of alternate and nonadjacent logical sectors of said assigned logical track of said logical disk unit, and

writing applied bytes representing another virtual record of the other virtual track, of the same pair of virtual tracks that contains said first virtual record into the logical sectors of said logical track that do not contain bytes of said first virtual record and that are intermediate and adjacent the logical sectors of said logical track that do contain bytes of said first virtual record,

said writing being effected in said interleaved manner so that adjacent sectors of said logical track contain bytes of different virtual records from said pair of virtual tracks of a single virtual cylinder.

21. The method of claim 20 wherein said bytes of said virtual records include information specifying the length of data fields of said virtual records and wherein said bytes of each virtual record are written into a plurality of logical sectors equal in number to that required to store all bytes comprising each such virtual record.

22. The method of claim 21 wherein said logical disk unit comprises a controller and a logical physical disk unit and wherein said controller responds to the reception by said logical unit of said bytes from said computer and applies commands in a fixed length sector format to said logical physical disk unit to control the logical sector of said logical physical disk unit into which each byte of a virtual record received from said computer is to be written.

23. The method of claim 22 wherein said commands applied by said computer to said logical disk unit to control an operation of said logical unit are identical to commands sent by said computer to a virtual system to control an operation corresponding to that performed by said logical unit in response to the reception of said identical commands from said computer.

24. A method of operating a logical data storage system adapted to emulate the physical and operational characteristics of a large capacity vendor unique virtual data storage disk drive system capable of supporting records having variable length data fields, said logical data storage system comprising:

a plurality of n sequentially arranged industry standard commodity disk drives arranged to form a logical disk storage unit connected to a computer via a data channel for the exchange of data between said computer and said logical data storage system, said method comprising the steps of;

operating said computer to apply to said logical system standard commands of said large capacity vendor unique virtual disk drive, and

operating said logical system in response to a reception of said standard commands for emulating command bytes, gaps, and variable length data fields of said large capacity vendor unique virtual disk drive using only standard commands, gaps, and fixed length data fields of said sequentially arranged commodity disk drives wherein the physical size of the virtual records written to said logical disk storage unit can be of a variable length,

said system being effective to interleave received bytes of different virtual tracks onto a single logical track of said logical unit.

25. The method of claim 24 wherein a correspondence does not exist between the physical size of said virtual records written to said emulated virtual disk drive and the size of the logical sectors written to the physical commodity disk drives comprising said logical storage unit.

26. The method of claim 24 wherein key and or data fields can be written by said logical storage unit for a virtual record normally written to said emulated virtual disk drive.

27. The method of claim 24 wherein said logical storage unit includes a parity disk drive that achieves a mean time between failure for said logical unit that exceeds the mean time between failure of said emulated virtual disk drive.

28. The method of claim 24 wherein higher speed channel data transfer rates can be supported by said logical unit exclusive of a cached disk control unit and

wherein data transfer rates can be executed by said system at speeds limited only by the speed capabilities of said channel.

29. The method of claim 24 wherein head switching within a cylinder of said logical unit is performed without performance loss or lost revolutions of a recording medium comprising said logical unit.

30. The method of claim 24 wherein updates of virtual records stored on said logical unit are executed directly on said commodity disk drives comprising said logical unit during write operations to said logical unit.

31. The method of claim 24 wherein all read and write operations by said logical unit are executed with said commodity disk drives comprising said logical unit synchronized to said channel.

32. The method of claim 24 wherein multiple virtual tracks of said virtual system are contained on one logical track of said logical unit.

33. The method of claim 24 wherein occurrences of single cylinder seek operations within said logical unit are reduced by the number of multiple virtual tracks contained on one logical track of said logical unit as compared to the number of cylinder seek operations required by said virtual system.

34. The method of claim 24 wherein the actual number of physical cylinders traversed by said logical unit as compared to said virtual system in response to the reception of a command by said logical unit from said computer is determined by dividing the number of virtual cylinders of said virtual disk drive by the number of virtual tracks contained on one logical track of said logical unit.

35. A method of operating a logical data storage system adapted to emulate the physical and operational characteristics of a large capacity vendor unique virtual data storage disk drive system capable of supporting records having variable length data fields, said logical data storage system comprising;

a plurality of n sequentially arranged industry standard commodity disk drives arranged to form a logical disk storage unit connected to a computer via a data channel for the exchange of data between said computer and said logical data storage system, said method comprising the steps of;

operating said computer to apply to said logical system standard commands of said large capacity vendor unique virtual disk drive,

operating said logical system in response to a reception of said standard commands for emulating command bytes, gaps, and variable length data fields of said large capacity vendor unique virtual disk drive using only standard commands, gaps, and fixed length data fields of said sequentially arranged commodity disk drives wherein the physical size of the virtual records written to said logical storage unit can be of a variable length,

assigning pairs of virtual tracks of virtual cylinders of said virtual system to a single logical track of a logical cylinder of said logical unit for the storage by said logical unit of the bytes of virtual records on said virtual tracks, each pair of virtual tracks being assigned to a different one of said logical tracks,

applying commands from said computer to said logical unit specifying the virtual cylinder and head and record number of a first virtual record for which data bytes are to be written into an assigned logical track of said logical unit,

operating said logical unit in response to the receipt of said commands specifying said virtual cylinder and head and record number for said first virtual record for which said data bytes are to be written to identify the area of said logical track where said bytes of said first virtual record are to be written,

sending a command from said logical disk unit to said computer when said logical unit is in an operational position corresponding to said first virtual record on said logical track,

applying said bytes to be written of said first virtual record from said computer via said channel to said logical disk unit,

writing said applied bytes of said first virtual record into the location of said identified logical track where said bytes of said first virtual record are to be written,

said writing being effected an interleaved manner that said bytes of said first virtual record are written into a plurality of alternate and nonadjacent logical sectors of said assigned logical track of said logical disk unit, and

writing applied bytes representing another virtual record of the other virtual track, of the same pair of virtual tracks that contains said first virtual record, into the logical sectors of said logical track that do not contain bytes of said first virtual record and that are intermediate and adjacent the logical sectors of said logical track that do contain bytes of said first virtual record,

said writing being effected in said interleaved manner so that adjacent sectors of said logical track contain bytes of different virtual records from said pair of virtual tracks of a single virtual cylinder.

36. In a logical data storage system connected to a computer via a data channel for an exchange of data between said computer and said logical storage system, said storage system comprising;

a parity storage unit and n sequentially arranged data storage units comprising a logical data storage unit,

means for receiving segments of virtual data records of different virtual tracks from said computer via said channel,

means for sequentially distributing received segments of a virtual record to said n data storage units so that each received segment is distributed to a single data storage unit and so that all of said n data storage units together receive segments comprising the entirety of said record,

means for generating a parity segment representing the parity of each group of n received segments in response to the distribution of said each group of n segments of said virtual record to said n units,

means for distributing each generated parity segment to said parity unit, and

means for interleaving received segments of different virtual tracks onto a single logical track of said logical unit by writing each distributed segment into the unit to which said segment is distributed so that the segments of virtual records of a first virtual track are written into alternate and non adjacent logical sectors of a single logical track and so that the logical sectors of said single logical track not containing bytes of said first virtual track are written to contain bytes of another virtual track.

37. The system of claim 36 in which each of said virtual records comprises a plurality of fields separated by gaps and wherein each of said logical sectors serves the dual function of storing segments of a virtual record of one virtual track while simulating a gap of a virtual record of another virtual track.

38. The system of claim 37 wherein each of said virtual tracks are on the same virtual cylinder.

39. The system of claim 38 wherein said logical device emulates the physical characteristics of a virtual device containing said virtual records.

40. A logical data storage system connected to a computer via a data channel for the exchange of data between said computer and said logical data storage system, said logical data storage system comprising;

n sequentially arranged data storage units forming a logical data storage unit and a parity storage unit,

means for receiving bytes of virtual data records of at least two different virtual tracks from said computer via said channel, each of said records having a plurality of fields separated by gaps,

means for sequentially distributing received bytes of each virtual record to said sequentially arranged n data storage units so that each received byte is distributed to a single data storage unit and so that all of said n data storage units together receive bytes comprising the entirety of said each virtual record,

means for generating a parity byte representing the parity of each group of n received bytes of a virtual record in response to the distribution of said each group of n bytes to said n data storage units,

means for distributing each generated parity byte to said parity unit concurrently with the distribution of the last byte of the group of n bytes from which said parity byte is generated, and

means for interleaving received bytes of different virtual tracks onto a single logical track of said logical data storage unit by writing each distributed byte into the data storage unit to which said byte is distributed so that the bytes of virtual records of a first virtual track are written into a plurality of alternate and nonadjacent logical sectors of a single logical track comprising a corresponding track of each of said n data storage units, said writing being effected in such a manner so that adjacent sectors of said logical track contain bytes of virtual records from different virtual tracks and so that each logical sector serves the dual function of storing data bytes of a virtual record of one virtual track and for simulating a gap for another virtual record of another virtual track.

41. A logical data storage system adapted to emulate a virtual data storage system, said logical storage system comprising;

a logical disk storage unit connected to a computer via a data channel for the exchange of data between said computer and said logical data storage system,

means for receiving bytes of virtual records of different virtual tracks from said computer via said channel,

means for applying received bytes of each virtual record to said logical disk unit, and

means for interleaving received bytes of different virtual tracks onto a single logical track of said logical unit by writing received bytes representing a first virtual record of a first virtual track into a plurality of alternate and nonadjacent logical sectors of a single logical track of said logical disk unit, and

means for writing received bytes representing another virtual record of another virtual track into the logical sectors of said logical track that do not contain bytes of said first logical record and that are intermediate and adjacent the logical sectors of said logical track that do contain bytes of said first virtual record,

said writing being effected in said interleaved manner so that adjacent sectors of said logical track contain bytes of different virtual records from said different virtual tracks.

42. The system of claim 41 wherein said different virtual tracks are on the same virtual cylinder of a virtual disk unit containing said virtual tracks.

43. The system of claim 41 wherein;

said logical disk unit comprises n different data storage disk units spindle synchronized so as to maintain rotational synchronization,

said means for applying comprises means for sequentially distributing the received bytes of each virtual record to said n units so that each received byte is distributed to a single unit and so that all of said n units together receive the bytes comprising the entirety of each received virtual record, and

said means for writing comprises means for writing each distributed byte into the unit to which said byte is distributed.

44. The system of claim 43 in which said system further comprises means responsive to the distribution of a byte to each of said n units for generating a parity byte representing said bytes received by each of said n units, and

means for writing said parity byte into a parity unit.

45. The system of claim 41 wherein each of said virtual records comprises a plurality of fields adjacent to each other on the virtual track containing said each record with each of said fields of a virtual record being separated from an adjacent field by a gap characterized by a plurality of byte times, and

wherein each of said virtual records is written into alternate sectors of said logical track so that the byte times comprising said gaps for a first one of said virtual records of a first virtual track are simulated by logical sectors of said logical track that do not contain bytes of the virtual track containing said first virtual record but that do contain bytes of another virtual record of another virtual track.

46. The system of claim 45 wherein at least one field of each virtual record comprises a data field whose length is dependant upon the quantity of bytes in said data field so that the length of the data field of a first virtual record can differ from the length of the data field of another virtual record, and wherein said system further comprises;

means for writing bytes of the data field of a virtual record into said logical sectors of a logical record with the number of logical sectors required for the writing of said data bytes being determined by the quantity of bytes in said virtual data field.

47. A logical data storage system adapted to emulate a virtual data storage system, said logical storage system comprising;

a logical disk storage unit connected to a computer via a data channel for the exchange of data between said computer and said logical data storage system,

means for receiving bytes of virtual records of different virtual tracks from said computer via said channel,

means for applying received bytes of each virtual record to said logical disk unit,

means for interleaving received bytes of different virtual tracks onto a single logical track of said logical unit by writing received bytes representing a first virtual record of a first virtual track into a plurality of alternate and nonadjacent logical sectors of a single logical track of said logical disk unit, and

means for writing received bytes representing another virtual record of another virtual track into the logical sectors of said logical track that do not contain bytes of said first logical record and that are intermediate and adjacent the logical sectors of said logical track that do contain bytes of said first virtual record,

said writing being effected in an interleaved manner so that adjacent sectors of said logical track contain bytes of different virtual records from said different virtual tracks,

said virtual records being recorded on said logical track in such a manner that;

a first sector on said logical track contains information for a first gap of a first virtual record of a first virtual track and a first gap of a second virtual record of a second virtual track,

a second sector adjacent to said first sector on said logical track contains home address information of both said first and second virtual records,

a third sector adjacent to said second sector on said logical track contains a count field of said first virtual record of said first virtual track,

a fourth sector adjacent to said third sector on said logical track contains a count field of said second virtual record of said second virtual track,

subsequent sectors of said logical track contain other fields of virtual records including said first and second virtual records of said first and second virtual tracks so that said fields of said first and second virtual records are interleaved on said logical track with adjacent fields of said logical track containing bytes of virtual records of different virtual tracks.

48. A logical data storage system adapted to emulate a virtual data storage system, said logical data storage system comprising a logical disk unit connected to a computer via a data channel for the exchange of data between said computer and said logical data storage system, said logical data storage system further comprising;

means for receiving bytes of virtual records of different virtual tracks from said computer via said channel with said records having a plurality of fields separated by gaps,

means for applying received bytes of each virtual record to said logical disk unit, and

means or interleaving received bytes of different virtual tracks onto a single logical track of said logical disk unit by writing said received bytes representing said virtual records into different logical sectors of a single logical track of said logical disk unit so that each logical sector serves the dual function of storing bytes of a virtual record of one of said virtual tracks as well of simulating a gap time for a virtual record of another virtual track.

49. The system of claim 48 wherein said writing is effected in such a manner that received bytes representing a first virtual record of a first virtual track are written into a plurality of alternate and nonadjacent logical sectors of said single logical track of said logical disk unit and so that bytes representing another virtual record of a different virtual tack are written into the logical sectors of said logical track not containing the bytes of said first virtual record,

said writing being effected in such a manner so that adjacent sectors of said logical track contain bytes of different virtual records from said different virtual tracks.

50. The system of claim 49 wherein said different virtual tracks are on the same virtual cylinder of a virtual disk unit containing said virtual track.

51. The system of claim 49 wherein;

said logical disk unit comprises n different data storage disk units spindle synchronized so as to maintain rotational synchronization,

and wherein said means for applying comprises means for sequentially distributing the received bytes of each virtual record to said n units so that each received byte is distributed to a single unit and so that all of said n units together receive the bytes comprising the entirety of each received virtual record, and

said means for writing comprises means for writing each received byte into the unit to which said byte is distributed.

52. The system of claim 48 wherein each of said virtual records comprises a plurality of fields adjacent to each other on the virtual track containing said each record with each of said fields being separated from an adjacent field by a gap characterized by a plurality of byte tines, and

wherein each of said virtual records is written into alternate logical sectors of said logical track so that byte times representing said gaps for a first one of said virtual records are simulated by sectors of said logical track that do not contain bytes of said first virtual record.

54. The system of claim 48 wherein at least one field of each virtual record comprises a data field whose length is dependant upon the quantity of data bytes in said field so that the length of the data field of a first virtual record can differ from the length of the data field another virtual record, and wherein said system further comprises;

means for writing bytes of a data field of a virtual record into the number of sectors of a logical record with the number of logical sectors required for the writing of said data bytes being determined by the quantity of bytes in said virtual data field.

53. A logical data storage system adapted to emulate a virtual data storage system, said logical data storage system comprising a logical disk unit connected to a computer via a data channel for the exchange of data between said computer and said logical data storage system, said logical data storage system further comprising;

means for receiving bytes of virtual records of different virtual tracks from said computer via said channel with said records having a plurality of fields separated by gaps,

means for applying received bytes of each virtual record to said logical disk unit, and

means for interleaving received bytes of different virtual tracks onto a single logical track of said logical unit by writing said received bytes representing said virtual records into different logical sectors of a single logical track of said logical disk unit so that each logical sector serves the dual function of storing bytes of a virtual record of one of said virtual tracks as well of simulating a gap time for a virtual record of another virtual track,

said virtual records being recorded on said logical track in such a manner that;

a first sector on said logical track contains information for a first gap of a first virtual record of a first virtual track and a first gap of a second virtual record of a second virtual track,

a second sector adjacent to said first sector on said logical track contains home address information of both said first and second virtual records,

a third sector adjacent to said second sector on said logical track contains a field of said first virtual record of said first virtual track,

a fourth sector adjacent to said third sector on said logical track contains a field of said second virtual record of said second virtual track,

alternate subsequent and nonadjacent sectors of said logical tack contain other fields of virtual records including said first and second virtual records of said first and second virtual tracks so that the fields of said first and second virtual records are interleaved on said logical track with adjacent fields of said logical track containing bytes of virtual records of different virtual tracks.

55. A logical data storage system adapted to emulate a virtual data storage system, said logical storage system comprising;

a logical disk storage unit connected to a computer via a data channel for the exchange of data between said computer and said logical data storage system,

means for assigning pairs of virtual tracks of virtual cylinders of said virtual data storage system to a single logical track of a logical cylinder of said logical unit for the storage by said logical disk unit of bytes of virtual records on said virtual tracks, each of said pairs of virtual tracks being on the same virtual cylinder and each pair of virtual tracks being assigned to a different one of said logical tracks,

means for applying commands from said computer to said logical disk unit specifying the virtual cylinder and head and record number of a first virtual record for which updated data bytes are to be written into an assigned logical track of said logical disk unit,

means for operating said logical disk unit in response to the receipt of said commands specifying said virtual cylinder and head and record number for said first virtual record for which said updated data bytes are to be written to identify the area of said logical track containing said first virtual record,

means for sending a command from logical disk unit to said computer when said logical disk unit is in an operational position corresponding to said first virtual record on said logical track,

means for applying said updated bytes of said first virtual record from said computer via said channel to said logical disk unit,

means for writing said applied updated bytes of said first virtual record into the location of said identified logical track containing said first virtual record,

said writing being effected in such a manner that said updated bytes of said first virtual record are written into a plurality of alternate and nonadjacent logical sectors of said assigned logical track of said logical disk unit, and

means for writing applied bytes representing another virtual record of the other virtual track of the same pair of virtual tracks that contains said first virtual record, into the logical sectors of said logical track that do not contain bytes of said first virtual record and that are intermediate and adjacent the logical sectors of said logical track that do contain bytes of said first virtual record,

said writing being effected in an interleaved manner so that adjacent sectors of said logical track contain bytes of different virtual records from said pair of virtual tracks of a single virtual cylinder.

56. The system of claim 55 wherein said bytes of said virtual records include information specifying the length of data fields of said virtual records and wherein said bytes of each virtual record are written into a plurality of logical sectors equal in number to that required to store all bytes comprising each such virtual record.

57. The system of claim 56 wherein said logical disk unit comprises a controller and a logical physical disk unit and wherein said controller responds to the reception by said logical disk unit of said bytes from said computer and applies commands in a fixed length sector format to said logical physical disk unit to control the logical sector of said logical physical disk unit into which each byte of a virtual record received from said computer is to be written.

58. The system of claim 57 wherein said commands applied by said computer to said logical disk unit to control an operation of said logical unit are identical to commands sent to said computer to a virtual system to control an operation corresponding to that performed by said logical unit in response to the reception of said identical commands from said computer.

59. A logical data storage system adapted to emulate the physical and operational characteristics of a large capacity vendor unique virtual data storage disk drive system capable of supporting records having variable length data fields, said logical data storage system comprising;

a plurality of n sequentially arranged industry standard commodity disk drives arranged to form a logical disk storage unit connected to a computer via a data channel for the exchange of data between said computer and said logical data storage system,

means for operating said computer to apply to said logical system standard commands of said large capacity vendor unique virtual disk drive, and

means for operating said logical system in response to a reception of said standard commands for emulating the command bytes, gaps, and variable length data fields of said large capacity vendor unique virtual disk drive using only standard commands, gaps, and fixed length data fields of said sequentially arranged commodity disk drives wherein the physical size of the virtual records written to said logical disk storage unit can be of a variable length,

said system being effective to interleave received bytes of different virtual tracks onto a single logical track of said logical disk storage unit.

60. The system of claim 69 wherein a correspondence does not exist between the physical size of said virtual records written to said emulated virtual disk drive and the size of the logical sectors written to the physical commodity disk drives comprising said logical disk storage unit.

61. The system of claim 59 wherein key and or data fields can be written by said logical storage unit for a virtual record normally written to said emulated virtual disk drive.

62. The system of claim 59 wherein said logical storage unit includes a parity disk drive that achieves a mean time between failure of said logical unit that exceeds the mean time between failure of said emulated virtual disk drive.

63. The system of claim 59 wherein higher speed channel data transfer rates can be supported by said logical unit exclusive of a cached disk control unit and

wherein data transfer rates can be executed by said system at speeds limited only by the speed capabilities of said channel.

64. The system of claim 59 wherein head switching within a cylinder of said logical unit is performed without performance loss or lost revolutions of a recording medium comprising said logical unit.

65. The system of claim 59 wherein updates of virtual records stored on said logical unit are executed directly on said commodity disk drives comprising said logical unit during write operations to said logical unit.

66. The system of claim 59 wherein all read and write operations by said logical unit are executed with said commodity disk drives comprising said logical unit synchronized to said channel.

67. The system of claim 59 wherein multiple virtual tracks of said virtual system are contained on one logical track of said logical unit.

68. The system of claim 59 wherein occurrences of single cylinder seek operations within said logical unit are reduced by the number of multiple virtual tracks contained on one logical track of said logical unit as compared to the number of cylinder seek operations required by said virtual system.

69. The system of claim 59 wherein the actual number of physical cylinders traversed by said logical unit as compared to said virtual system in response to the reception of a command by said logical unit from said computer is determined by dividing the number of virtual cylinders of said virtual disk drive by the number of virtual tracks contained on one logical track of said logical unit.

70. A logical data storage system adapted to emulate the physical and operational characteristics of a large capacity vendor unique virtual data storage disk drive system capable of supporting records having variable length data fields, said logical data storage system comprising;

a plurality of n sequentially arranged industry standard commodity disk drives arranged to form a logical disk storage unit connected to a computer via a data channel for the exchange of data between said computer and said logical data storage system,

means for operating said computer to apply to said logical system standard commands of said large capacity vendor unique virtual disk drive,

means for operating said logical system in response to a reception of said standard commands for emulating the command bytes, gaps, and variable length data fields of said large capacity vendor unique virtual disk drive using only standard commands, gaps, and fixed length data fields of said sequentially arranged commodity disk drives wherein the physical size of the virtual records written to said logical disk storage unit can be of a variable length,

means for assigning pairs of virtual tracks of virtual cylinders of said virtual system to a single logical track of a logical cylinder of said logical unit for the storage by said logical unit of the bytes of virtual records on said virtual tracks, each pair of virtual tracks being assigned to a different one of said logical tracks,

means for applying commands from said computer to said logical unit specifying the virtual cylinder and head and record number of a first virtual record for which data bytes are to be written into an assigned logical track of said logical unit,

means for operating said logical unit in response to the receipt of said commands specifying said virtual cylinder and head and record number for said first virtual record for which said data bytes are to be written to identify the area of said logical track where said bytes of said first virtual record are to be written,

means for sending a command from said logical disk unit to said computer when said logical unit is in an operational position corresponding to said first virtual record on said logical track,

means for applying said bytes to be written of said first virtual record from said computer via said channel to said logical disk unit,

means for writing said applied bytes of said first virtual record into the location of said identified logical track where said bytes of said first virtual record are to be written,

said writing being effected in an interleaved manner that said bytes of said first virtual record are written into a plurality of alternate and nonadjacent logical sectors of said assigned logical track of said logical disk unit, and

means for writing applied bytes representing another virtual record of the other virtual track, of the same pair of virtual tracks that contains said first virtual record, into the logical sectors of said logical track that do not contain bytes of said first virtual record and that are intermediate and adjacent the logical sectors of said logical track that do contain bytes of said first virtual record,

said writing being effected in said interleaved manner so that adjacent sectors of said logical track contain bytes of different virtual records from said pair of virtual tracks of a single virtual cylinder.