Reverse directory structure in a garbage collection unit (GCU)

An apparatus comprising:

• a non-volatile memory (NVM) comprising a plurality of semiconductor memory dies;
• a data manager circuit configured to form a write stream of user data blocks to be written to a garbage collection unit (GCU) of the NVM;
• a reverse directory manager circuit configured to generate an entry of a reverse directory footer for each user data block in the write stream to describe a physical address in the GCU at which the corresponding user data block is to be stored;
• and
• a buffer memory configured to accumulate the entries generated by the reverse directory manager circuit until a total predetermined number of entries is reached to form a complete footer data structure, the reverse directory manager circuit further configured to insert the complete footer data structure into the write stream for writing to the GCU with the user data blocks, the complete footer data structure having an overall size that corresponds to an overall size of each of the user data blocks;
• and
• a write circuit configured to, responsive to receipt of the write stream, write a plurality of the complete footer data structures and the associated user data blocks to the GCU so that each successive pair of first and second complete footer data structures are separated by an intervening number of user data blocks described by the second complete footer data structure.

A solid-state drive (SSD), comprising:

• a non-volatile memory (NVM) characterized as a flash memory comprising a plurality of semiconductor memory dies, each die comprising flash memory cells arranged into a plurality of erasure blocks with each erasure block constituting a smallest grouping of the flash memory cells that can be concurrently erased;
• a controller circuit configured to form a garbage collection unit (GCU) by grouping together a selected erasure block from each of a subset of the dies in the NVM, the GCU allocated and erased as a unit;
• a data manager circuit configured to form a write stream of user data blocks to be written to the GCU, each user data block having X total bytes of user data;
• a reverse directory manager circuit configured to generate an entry of a reverse directory footer for each user data block in the write stream to describe a physical address in the GCU at which the corresponding user data block is to be stored, each entry having Y total bytes of map data;
• and
• a buffer memory configured to accumulate the entries generated by the reverse directory manager circuit until a total number of Z entries is reached to form a complete footer data structure where Z=X/Y, the reverse directory manager circuit further configured to insert the complete footer data structure into the write stream for writing to the GCU with the user data blocks, the complete footer data structure having an overall size that corresponds to an overall size of each of the user data blocks.