Abstract: The storage capacity of a Level Five RAID array on an initial set of disks is expanded by the steps of: A) adding to the rows of the array, new data blocks but no parity blocks which reside on an additional set of disks; and, B) initializing the new data blocks such that the exclusive-or of their content in each row of the array is zero. Due to these steps A) and B), the need to rewrite the original data blocks and parity blocks on the initial set of disks as part of the expansion process is eliminated, and thus the expansion of the array occurs quickly.

Abstract: A method of tracking incomplete writes in a disk array includes the steps of sequentially receiving a plurality of write commands which identify respective blocks in the array that are to be written; generating a list of expanded write areas for only those write commands which are received most recently, where each expanded write area encompasses the blocks that are to be written plus additional blocks which are likely to be written by subsequent write commands; modifying the list, each time a write command is subsequently received which writes a particular block that is not in any expanded write area in the list, by replacing one expanded write area with a new expanded write area that encompasses the particular block; and storing a replica of the list on a magnetic media each time the modifying step occurs.