Partial mirroring during expansion thereby eliminating the need to track the progress of stripes updated during expansion

A system, comprising:

• an array of disks, wherein each disk in said array of disks comprises a plurality of stripe units, wherein a stripe is a group of corresponding stripe units from each disk in said array of disks;
• and
• a controller coupled to said array of disks, wherein said controller is configured to manage said array of disks, wherein said controller comprises:
• a memory unit operable for storing a program for performing an expansion of said array of disks;
• and
• a processor coupled to said memory, wherein said processor, responsive to said program, comprises:
• circuitry operable for rebuilding stripe units in a disk in said array of disks stripe by stripe;
• circuitry operable for receiving a request to write data to a particular stripe unit in said disk during an expansion process;
• circuitry operable for writing said data in said particular stripe unit in said disk if said particular stripe unit was rebuilt during said expansion process;
• and
• circuitry operable for mirroring said data to a stripe unit that corresponds to said particular stripe unit in a same stripe if said particular stripe unit was rebuilt during said expansion process, wherein said mirror stripe unit is located in another disk of said array of disks.

A system, comprising:

• means for rebuilding stripe units in a disk in said disk array stripe by stripe, wherein each disk in said disk array comprises a plurality of stripe units, wherein a stripe is a group of corresponding stripe units from each disk in said disk array;
• means for receiving a request to write data to a particular stripe unit in said disk during an expansion process;
• means for writing said data in said particular stripe unit in said disk if said particular stripe unit was rebuilt during said expansion process;
• and
• means for mirroring said data to a stripe unit that corresponds to said particular stripe unit in a same stripe if said particular stripe unit was rebuilt during said expansion process, wherein said mirror stripe unit is located in another disk of said disk array.

A computer program product embodied in a machine readable medium for performing an expansion of a disk array comprising the programming steps of:

• rebuilding stripe units in a disk in said disk array strip by stripe, wherein each disk in said disk array comprises a plurality of stripe units, wherein a stripe is a group of corresponding stripe units from each disk in said disk array;
• receiving a request to write data to a particular stripe unit in said disk during an expansion process;
• writing said data in said particular stripe unit in said disk if said particular stripe unit was rebuilt during said expansion process;
• and
• mirroring said data to a stripe unit that corresponds to said particular stripe unit in a same stripe if said particular stripe unit was rebuilt during said expansion process, wherein said mirror stripe unit is located in another disk of said disk array.