Data migration method for a storage system after expansion and storage system

A data migration method for a storage system after expansion, wherein the storage system comprises a controller, and one of the following:

• (a) vi-1 disks before an ith expansion, and
• (b) vi disks after the ith expansion,
• wherein i is greater than or equal to 1, the controller communicates with all disks, data is distributed on the disks in the storage system based on a parity declustering technology, and
• the method comprises:
• determining, by the controller, a quantity of chunks comprised in a migration unit for the ith expansion;
• dividing storage space of each of the vi-1 disks comprised in the storage system before the ith expansion into a plurality of migration units, wherein each migration unit comprises a foregoing quantity of chunks;
• determining, based on a quantity vi of disks comprised in the storage system after the ith expansion and a quantity vi-1 of disks comprised in the storage system before the ith expansion, an auxiliary balanced incomplete block design (BIBD) {circumflex over (B)}[i] required for data migration after the ith expansion;
• and
• selecting, based on the auxiliary BIBD {circumflex over (B)}[i], at least one migration unit from the plurality of migration units of the vi-1 disks before the ith expansion, and migrating chunks comprised in the selected at least one migration unit to one of the vi disks after the ith expansion.