Controller, storage apparatus, and computer program product

A storage apparatus comprising:

• a first data-storage unit that stores parity data of user data of which writing is requested by a host device;
• a second data-storage unit that stores the user data and the parity data;
• and
• a controller that controls writing into the first data-storage unit and the second data-storage unit, and reading from the first data-storage unit and the second data-storage unit, a storage area in the second data-storage unit in which user data is stored having a first state and a second state, the first state being a state that user data stored in the storage area is protected by the parity data stored by the first data-storage unit, the second state being a state that user data stored in the storage area is not protected by the parity data stored by the first data-storage unit, wherein the controller comprises
• a parity updating unit that updates the parity data when state of the storage area is changed, and writes first parity data into the first data-storage unit, the first parity data being the updated parity data, and
• a parity writing unit that reads the parity data written in the first data-storage unit and writes second parity data into the second data-storage unit at a timing determined independently from the timing of updating of the parity data, the second parity data being the read parity data.

A computer program product having a non-transitory computer readable medium including programmed instructions, wherein when executed by a computer that controls writing into and reading from a first data-storage unit and a second data-storage unit included in a storage apparatus, the first data-storage unit storing parity data of user data of which writing is requested by a host device, and the second data-storage unit storing the user data and the parity data, a storage area in the second data-storage unit in which user data is stored having a first state and a second state, the first state being a state that user data stored in the storage area is protected by the parity data stored by the first data-storage unit, the second state being a state that user data stored in the storage area is not protected by the parity data stored by the first data-storage unit the instructions cause the computer to function as:

• a parity updating unit that updates the parity data when state of the storage area is changed, and writes first parity data into the first data-storage unit, the first parity data being the updated parity data;
• and
• a parity writing unit that reads the parity data written in the first data-storage unit and writes second parity data into the second data-storage unit at a timing determined independently from the timing of updating of the parity data, the second parity data being the read parity data.