Operating a RAID array with unequal stripes
Operating a RAID array with unequal stripes, the RAID array comprising N number of drives, where each RAID stripe includes P number of parity drives and N-P number of data drives, including 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 N-P write groups, 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, in round-robin order, to the N-P write groups; calculating parity from the N-P write groups; and writing the N-P write groups and the calculated parity as a first RAID stripe to the RAID array.
1. A method of 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 method comprising:
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.
2. The method of claim 1 , wherein the write groups are written to corresponding data stripes of the first RAID stripe before writing data stripes of a second RAID stripe to the RAID array.
3. The method of claim 2 , wherein at least one data stripe of the second RAID stripe is written to a drive of the RAID array on which the parity stripe of the first RAID stripe resides.
4. The method of claim 1 , wherein a number of chunks that are of the sub-stripe size is greater than the N-P number of data drives.
5. The method of claim 1 , wherein the parity stripe of the first RAID stripe is written to a higher logical block address than the data stripes of the first RAID stripe.
6. The method of claim 1 , wherein writing the write groups and the calculated parity as the first RAID stripe to the RAID array further includes performing a single write operation to each drive of the RAID array.
7. The method of claim 1 , wherein the calculated parity is less than the parity stripe size.
8. 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.
9. The apparatus of claim 8 , wherein the write groups are written to corresponding data stripes of the first RAID stripe before writing data stripes of a second RAID stripe to the RAID array.
10. The apparatus of claim 9 , wherein at least one data stripe of the second RAID stripe is written to a drive of the RAID array on which the parity stripe of the first RAID stripe resides.
11. The apparatus of claim 8 , wherein a number of chunks that are of the sub-stripe size is greater than the N-P number of data drives.
12. The apparatus of claim 8 , wherein the parity stripe of the first RAID stripe is written to a higher logical block address than the data stripes of the first RAID stripe.
13. The apparatus of claim 8 , wherein writing the write groups and the calculated parity as the first RAID stripe to the RAID array further includes performing a single write operation to each drive of the RAID array.
14. The apparatus of claim 8 , wherein the calculated parity is less than the parity stripe size.
15. 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.
16. The computer program product of claim 15 , wherein the write groups are written to corresponding data stripes of the first RAID stripe before writing data stripes of a second RAID stripe to the RAID array.
17. The computer program product of claim 16 , wherein at least one data stripe of the second RAID stripe is written to a drive of the RAID array on which the parity stripe of the first RAID stripe resides.
18. The computer program product of claim 15 , wherein a number of chunks that are of the sub-stripe size is greater than the N-P number of data drives.
19. The computer program product of claim 15 , wherein the parity stripe of the first RAID stripe is written to a higher logical block address than the data stripes of the first RAID stripe.
20. The computer program product of claim 15 , wherein writing the write groups and the calculated parity as the first RAID stripe to the RAID array further includes performing a single write operation to each drive of the RAID array.