Importance

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Abstract

An I/O command block, that is stored in a memory, includes information for connecting the I/O command block to other I/O command blocks in a chain structure. The I/O command block chain structure allows simultaneity of execution, provides a mechanism to inhibit and enable execution of an individual I/O command block, and a mechanism for establishing precedence in the sequence of execution of the I/O command blocks. A plurality of I/O command blocks are configured into a chain of I/O command blocks in a memory where each I/O command block includes one of the plurality of I/O commands necessary to perform a RAID 5 I/O operation. A set of the I/O command blocks in the chain are configured so that the set of I/O command blocks are enabled to execute concurrently, i.e., the set of I/O command blocks are a concurrent string of I/O command blocks. The chain of I/O command blocks is executed in a sequence that is specified and controlled only by information in the I/O command blocks to perform the RAID 5 operation. For a RAID 5 write sequence, the string of concurrent I/O command blocks includes an I/O command block for a read data disk, and an I/O command block for a read parity disk. Also, one of the I/O command blocks in the chain is configured as an offshoot command block from one of the I/O command blocks in the string of concurrent I/O command blocks.

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First Claim