Storage device cache

A method of operating a mass storage device, the method comprising:

• caching data in nonvolatile semiconductor memory, the nonvolatile semiconductor memory having a predetermined usable lifetime;
• iteratively performing an operation on the nonvolatile semiconductor memory until the nonvolatile semiconductor memory reaches a predetermined state, wherein the operation comprises an erase operation or a program operation, and wherein iteratively performing the operation on the nonvolatile semiconductor memory until the nonvolatile semiconductor memory reaches the predetermined state comprises
• performing the iterations of the operation on a selected area of the nonvolatile semiconductor memory;
• performing a read of the selected area of the nonvolatile semiconductor memory after each of the iterations is performed;
• and
• ending performance of the iterations of the operation in response to the read indicating that the selected area of the nonvolatile semiconductor memory has reached the predetermined state, wherein the predetermined state corresponds to one of (i) a predetermined programmed state or (ii) a predetermined erased state;
• determining an extent to which the nonvolatile semiconductor memory has degraded in response to a number of iterations of the operation required for the nonvolatile semiconductor memory to reach the predetermined state;
• determining whether the nonvolatile semiconductor memory has reached the predetermined usable lifetime in response to the extent to which the nonvolatile semiconductor memory has degraded;
• and
• in response to the nonvolatile semiconductor memory having reached the predetermined usable lifetime, suspending the caching of data in the nonvolatile semiconductor memory.

A non-transitory computer readable medium storing a computer program, the computer program comprising instructions to cause a programmable processor to:

• cache data in nonvolatile semiconductor memory, the nonvolatile semiconductor memory having a predetermined usable lifetime;
• iteratively perform an operation on the nonvolatile semiconductor memory until the nonvolatile semiconductor memory reaches a predetermined state, wherein the operation comprises an erase operation or a program operation, and wherein the instructions to iteratively perform the operation on the nonvolatile semiconductor memory until the nonvolatile semiconductor memory reaches the predetermined state comprise instructions to
• perform the iterations of the operation on a selected area of the nonvolatile semiconductor memory;
• perform a read of the selected area of the nonvolatile semiconductor memory after each of the iterations is performed;
• and
• end performance of the iterations of the operation in response to the read indicating that the selected area of the nonvolatile semiconductor memory has reached the predetermined state, wherein the predetermined state corresponds to one of (i) a predetermined programmed state or (ii) a predetermined erased state;
• determine an extent to which the nonvolatile semiconductor memory has degraded in response to a number of iterations of the operation required for the nonvolatile semiconductor memory to reach the predetermined state;
• determine whether the nonvolatile semiconductor memory has reached the predetermined usable lifetime in response to the extent to which the nonvolatile semiconductor memory has degraded;
• and
• in response to the nonvolatile semiconductor memory having reached the predetermined usable lifetime, suspend the caching of data in the nonvolatile semiconductor memory.