Method and apparatus for synchronizing data from asynchronous disk drive data transfers

A method of reading data from a redundant array of independent disk drives comprising:

• for each disk drive in the redundant array, providing a corresponding FIFO memory arranged for receiving and storing read data using timing signals provided by the respective drive;
• initiating a READ command to each of the drives of the RAID array, thereby causing each of the drives to retrieve selected elements of its stored data, and to transfer the retrieved data from the drive into the corresponding FIFO memory using the timing signals provided by the respective drive;
• monitoring each of the FIFO memories to detect a non-empty condition, implying receipt of data in the FIFO memory from the corresponding disk drive;
• waiting until all of the FIFO memories indicate such a non-empty condition;
• then synchronously reading the stored data from all of the FIFO memories, thereby forming synchronous read data;
• writing the synchronous read data into a common buffer;
• and
• repeating said monitoring, waiting, reading and writing steps until completion of a read operation initiated by the READ command.

An improved RAID disk array controller comprising:

• a plurality of disk drive interfaces for attaching physical disk drives;
• a two-port memory associated with each of the disk drive interfaces, each two-port memory arranged to store read data provided by the associated disk drive in a disk read operation and, conversely, to provide write data that was previously-stored in the memory to the associated disk drive in a disk write operation;
• a logic circuit coupled to all of the two-port memories for detecting when all of the two-port memories have data stored therein for a read operation or available space therein for a write operation;
• control circuitry responsive to the logic circuit for synchronously reading data from all of the two-port memories only when all of the two-port memories have data stored therein, thereby forming synchronous read data;
• the control circuitry further responsive to the logic circuit for detecting that all of the two-port memories have space therein and synchronously writing data to all of the two port memories thereby forming synchronous write data;
• first redundant data circuitry for regenerating missing data “on the fly” from the synchronous read data in the event that one of the disk drives fails to provide read data to its associated two-port memory in a read operation;
• and
• second redundant data circuitry for generating redundant data “on the fly” from the synchronous write data for storing in the array.

A method of writing data into an array of independent disk drives, the method comprising:

• providing a buffer for storing write data;
• for each disk drive in the array, providing a corresponding two-port memory for receiving and storing write data, the two-port memory;
• monitoring each of the two-port memories to detect a non-full condition;
• waiting until all of the two-port memories indicate such a non-full condition;
• then reading write data from the buffer;
• computing redundant data from said write data;
• synchronously storing the write data and the redundant data into the two-port memories via a first port of each memory;
• and
• substantially concurrently, transferring stored data from a second port of each of the two-port memories into the corresponding disk drives, in each case transferring the data responsive to timing control provided by the respective disk drive.