Patent attributes
A subset of drives with protection groups that have D data members and P parity members is created with (D+P+1) drives each having (D+P) partitions. One of the protection groups is used for spare capacity. (D+P) sequentially numbered protection groups are created by distributing protection group members such that members of protection group (X+Y) modulo (D+P+1) are located on the partition at drive X of partition Y. Alternatively, members of protection group (X−Y) modulo (D+P+1) are located on the partition at drive X of partition Y. New drives are added in single drive increments. When a new drive is added the first (D+P) protection group members of the lowest numbered unrotated partition of the (D+P) lowest numbered drives are rotated onto the new drive. Members are rotated in ascending order by drive to locations in ascending order by partition. A new protection group is created in the partitions made available due to rotation. When there are enough drives in the drive subset to enable a split, then the drive subset is split into two drive subsets, e.g. a first drive subset of (D+P) drives and a second drive subset of (D+P+1) drives.
