Append-only storage in a disk array using striping and parity caching

A method for writing information to a stripe on an array of independent disks, the stripe comprising a series of blocks spanning the disks, the method comprising:

• determining whether data has been written to the stripe in a current pass;
• if the stripe has not been written to in the current pass, calculating a parity value for the stripe;
• caching the parity value, only if the information does not span a full stripe;
• adding zeroes to the information to form a full stripe;
• writing the information, including the zeroes, and the parity value to the stripe, one block of the information being stored on each disk;
• if the stripe has been written to in the current pass, retrieving the parity value cached in a previous write operation;
• calculating a new parity value based on the information and the cached parity value;
• caching the new parity value only if appending the information would not complete the stripe;
• updating a parity block on the stripe based on the new parity value;
• and
• appending the information to the stripe.

A method for writing information to a stripe on an array of independent disks, the stripe comprising a series of blocks spanning the disks, the method comprising:

• dividing the information into pages, each page being a smallest input/output unit for a disk in the array, and placing a monotonically increasing stamp in each page;
• determining whether the stripe has been written to in a current pass;
• if the stripe has not been written to in the current pass, calculating a parity value for the information;
• caching the parity value if the information does not span the stripe;
• writing the information and the parity value to the stripe, one block of the information being stored on each disk;
• if the stripe has been written to in the current pass, retrieving the parity value cached in a previous write operation;
• calculating a new parity value based on the information and the cached parity value;
• caching the new parity value only if appending the information to the stripe would not complete the stripe;
• updating a parity block on the stripe based on the new parity value;
• and
• appending the information to the stripe.