Flash-memory card for caching a hard disk drive with data-area toggling of pointers stored in a RAM lookup table

A method for caching data from a rotating disk in a non-volatile flash memory using a volatile lookup table comprising:

• intercepting a host request with a host logical-sector address (LSA) for host data stored in the rotating disk;
• finding a modulo-M remainder of the host LSA, wherein the volatile lookup table has M entries;
• selecting a selected entry in the volatile lookup table using the modulo-M remainder;
• reading from the selected entry a selected physical-block address (PBA) of a selected physical block in the non-volatile flash memory;
• searching for a page-match by reading a stored LSA for each page and comparing the stored LSA to the host LSA and signaling a page-match when valid bits for the page indicate that the stored LSA is valid;
• reading a data sector from a page having a stored LSA that generated the page-match in the selected physical block and sending the data sector to the host and disabling access to the rotating disk when the host request is a read;
• activating the rotating disk to return disk-read data to the host when no page-match is found and writing the disk-read data from the rotating disk to the non-volatile flash memory;
• and
• searching for an empty page in the selected physical block and writing host data to the empty page when the host request is a write, or writing the disk-read data from the rotating disk to the empty page when the host request is a read and no page-match is found;
• when the empty page in the selected physical block is not found, activating a toggle routine to copy data sectors stored in pages of the selected physical block to the rotating disk and to erase the selected physical block, and to select a new selected physical block having an empty page to write the host data or the disk-read data from the rotating disk to the empty page,
• whereby data areas are toggled when the new selected physical block is selected by the toggle routine.

A method for restoring a volatile lookup table for a non-volatile cache of a rotating disk after power is interrupted comprising:

• selecting a current entry from among M entries in the volatile lookup table;
• (a) reading a first logical-sector address (LSA) from each first physical block in a first data area of a flash-memory array, and finding a first modulo-M remainder of the first LSA, and when the first modulo-M remainder matches an identifier for the current entry in the volatile lookup table, reading a first history counter from the physical block;
• reading a second LSA from each second physical block in a second data area of the flash-memory array, and finding a second modulo-M remainder of the second LSA, and when the second modulo-M remainder matches the identifier for the current entry in the volatile lookup table, reading a second history counter from the physical block;
• comparing the first history counter to the second history counter;
• writing a mapping to the first physical block to the current entry in the volatile lookup table when the first history counter indicates a count value that was more recently updated than the second history counter;
• writing a mapping to the second physical block to the current entry in the volatile lookup table when the second history counter indicates a count value that was more recently updated than the first history counter;
• selecting another current entry from among the M entries in the volatile lookup table and repeating from (a) until all M entries in the volatile lookup table have been processed,
• whereby the volatile lookup table is restored from the flash-memory array in the non-volatile cache.