Non-volatile memory with scheduled reclaim operations
In a non-volatile memory array, scheduling of reclaim operations to occur before a shortage of erased blocks arises avoids extended periods of reclaim that could exceed a time limit. A memory controller uses information regarding the data stored in the memory array to estimate the additional host data that may be programmed and the reclaim operations to be performed and schedules the reclaim operations to be evenly distributed between write operations until the memory is full.
1. A memory system, comprising:
a non-volatile memory array that includes a plurality of blocks, a block being the minimum unit of erase;
a memory controller operable to maintain a record of logical-to-physical mapping for host data stored in the non-volatile memory array, the record having a plurality of entries, an individual entry indicating a logical address by a unique file identifier and an offset, the memory controller further operable to determine whether stored data is valid or obsolete according to information supplied by a host, the memory controller further operable to copy valid data at a rate that depends on the amount of data to be copied to reclaim remaining reclaimable space and on the total amount of additional host data that may be written before the memory array becomes full.
2. The memory system of claim 1 wherein the memory controller is further operable to calculate the rate in response to a host command.
3. The memory system of claim 1 wherein the memory controller is further operable to calculate the rate to provide a constant rate of programming of host data until the memory is filled with valid host data.
4. The memory system of claim 1 wherein the memory system is embodied in a removable memory card that is operable to communicate with the host through a standard interface.
5. The memory system of claim 1 wherein the information supplied by the host includes information regarding host files using unique file identifiers to refer to host files.
6. The memory system of claim 1 wherein the memory controller is further operable to determine the rate by an interactive ratio.
7. The memory system of claim 6 wherein the interactive ration is the ration of (a) programming of host data received from a host to the non-volatile memory to (b) copying of previously stored valid data from one block to another.