Operating a RAID array with unequal stripes

An apparatus for operating a redundant array of independent disks (RAID) array, the RAID array comprising N number of drives to which data is written in RAID stripes, where each RAID stripe includes P number of parity drives that store parity in parity stripes and N-P number of data drives that store data in data stripes, the apparatus comprising a computer processor and a computer memory having disposed within it computer program instructions that, when executed by the computer processor, cause the apparatus to carry out the steps of:

• buffering, by a RAID controller, write operations received from a host, each write operation specifying data to be written to the RAID array;
• distributing, by the RAID controller, the data to be written amongst the data drives of a first RAID stripe of the RAID array, including:
• dividing the data into chunks of a sub-stripe size, wherein the sub-stripe size is less than a parity stripe size;
• and
• assigning the chunks to write groups in a repeating pattern, each write group corresponding to a particular data drive of the first RAID stripe, the pattern including assigning respective first chunks to each write group in consecutive order beginning with a first data drive, assigning respective second chunks to each write group in consecutive order beginning with the first data drive, and so on such that each write group includes non-consecutive sub-stripe sized chunks of data;
• calculating parity from the write groups;
• and
• writing the write groups and the calculated parity as the first RAID stripe to the RAID array, including:
• writing each write group as a data stripe to a corresponding data drive of the first RAID stripe;
• and
• writing the calculated parity as a parity stripe to a corresponding parity drive of the first RAID stripe.

A computer program product for operating a redundant array of independent disks (RAID) array, the RAID array comprising N number of drives to which data is written in RAID stripes, where each RAID stripe includes P number of parity drives that store parity in parity stripes and N-P number of data drives that store data in data stripes, the computer program product comprising a non-transitory computer readable storage medium comprising computer readable program instructions stored thereon, the program instructions executable to cause a computer to carry out the steps of:

• buffering, by a RAID controller, write operations received from a host, each write operation specifying data to be written to the RAID array;
• distributing, by the RAID controller, the data to be written amongst the data drives of a first RAID stripe of the RAID array, including:
• dividing the data into chunks of a sub-stripe size, wherein the sub-stripe size is less than a parity stripe size;
• and
• assigning the chunks to write groups in a repeating pattern, each write group corresponding to a particular data drive of the first RAID stripe, the pattern including assigning respective first chunks to each write group in consecutive order beginning with a first data drive, assigning respective second chunks to each write group in consecutive order beginning with the first data drive, and so on such that each write group includes non-consecutive sub-stripe sized chunks of data;
• calculating parity from the write groups;
• and
• writing the write groups and the calculated parity as the first RAID stripe to the RAID array, including:
• writing each write group as a data stripe to a corresponding data drive of the first RAID stripe;
• and
• writing the calculated parity as a parity stripe to a corresponding parity drive of the first RAID stripe.