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Method and apparatus for synchronizing disk drive requests within a disk array
| Details |
Inventors: Jibbe, Mahmoud K.; McCombs, Craig C.;
Assignee: NCR Corporation (Dayton, OH)
Primary Examiner: Robertson; David L.
Assistant Examiner:
Attorney, Agent or Firm: Stover; James M.
A simple method and circuit for qualifying and combining individual request signals received from a plurality of disk drives within a disk array to generate a single, synchronized request signal for the disk array. The circuit includes an activity register for storing a bit pattern which identifies those disk drives which are in use within the array. Each bit position within the activity corresponds to a different disk drive within the disk array. A logic one stored in a bit position identifies the disk drive corresponding to the bit position as being active while a logic zero stored in a bit position identifies the disk drive corresponding to the bit position as being inactive. The circuit further includes an OR gate associated with each disk drive within the disk array, each OR gate having a first input connected to receive the bit information corresponding to its associated disk drive from the activity register, and a second inverting input for receiving the individual request signal from its associated disk drive. The outputs of the OR gates are provided to an AND logic operator which combines the received signals to generate the request signal for the array. Additionally, the circuit includes a NAND gate associated with each disk drive within the disk array. Each NAND gate has a first input connected to receive the bit corresponding to its associated disk drive from the activity register, and a second input for receiving an acknowledge signal for the disk array. The NAND gates function to provide individual acknowledge signals to the active disk drives within the array. |
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DETAILED DESCRIPTION There is provided, in accordance with the present invention, a method and apparatus for generating a single request signal for a logical storage unit including all or a subset of all the disk drives within a disk array.
The apparatus includes an activity register for storing a bit pattern which identifies those disk drives included within the logical storage unit, and logic connected to receive the bit pattern stored within the activity register and individual request signals from each disk drive within the disk array.
The logic combines the individual request signals associated with the disk drives included within the logical storage unit, ignoring signals received from those drives not identified as included within the logical storage unit, to generate the single request signal for the logical storage unit.
In the described embodiment, the activity register is loaded with a bit pattern which includes a bit corresponding to each disk drive within the disk array.
A logic one stored in a bit position identifies the disk drive corresponding to the bit position as being active, i.
e.
, included within the logical storage unit.
A logic zero stored in a bit position identifies the disk drive corresponding to the bit position as being inactive, i.
e.
, not included within the logical storage unit.
The logic for combining the individual request signals comprises an OR gate associated with each disk drive within the disk array, each OR gate having a first input connected to receive the bit corresponding to its associated disk drive from the activity register, and a second inverting input for receiving the individual request signal from its associated disk drive.
The outputs of the OR gates are provided to an AND logic operator which combines the received signals to generate the request signal for the logical unit.
Additionally, the apparatus includes a NAND gate associated with each disk drive within the disk array.
Each NAND gate has a first input connected to receive the bit corresponding to its associated disk drive from the activity register, and a second input for receiving an acknowledge signal for the logical storage unit
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I/O Systems 
