Reliable RAID System with Embedded Spare Capacity and Flexible Growth

An apparatus, comprising:

• a plurality of non-volatile drives;
• a plurality of interconnected compute nodes that manage access to the drives;
• and
• a drive manager configured to:
• create (D+P) partitions that are equal in size and number on (D+P+1) drives;
• create protection groups that have D data members and P parity members by symmetrically distributing the protection group members on the partitions using modulo arithmetic;
• individually add new drives with (D+P) partitions equal in size and number to the partitions of the (D+P) drives;
• for each of the new drives:
• select (D+P) protection group members located on an unrotated partition of the (D+P) drives;
• rotate the (D+P) selected protection group members from the unrotated partition to the new drive;
• and
• create a new protection group using partitions freed by rotating the selected protection group members to the new drive.

A computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method for using a computer system to scale a subset of drives, the method comprising:

• creating (D+P) partitions that are equal in size and number on (D+P+1) drives;
• creating protection groups that have D data members and P parity members by symmetrically distributing the protection group members on the partitions using modulo arithmetic;
• individually adding new drives with (D+P) partitions equal in size and number to the partitions of the (D+P) drives;
• for each of the new drives:
• selecting (D+P) protection group members located on an unrotated partition of the (D+P) drives;
• rotating the (D+P) selected protection group members from the unrotated partition to the new drive;
• and
• creating a new protection group using partitions freed by rotating the selected protection group members to the new drive.