Sandisk Technologies Inc.

Manoj M Shenoy

Lakshmi Sowjanya Sunkavelli

Ramanathan Muthiah

Gopu S

Niranjani Rajagopal

A multi-tier memory comprises a block of memory with a plurality of sub-blocks (e.g., three sub-blocks). A garbage collection operation that chooses a source block based on a valid fragment count may not be suitable in multi-tier memories where sub-blocks have a dependency on one another (e.g., for an erase or program operation). The embodiments presented herein provide various garbage collection techniques that can be used in this situation. The techniques described herein can take in to account the valid fragment count of various sub-block groupings when deciding where to perform a garbage collection operation.

Data storage device and method for garbage collection in a multi-tier memory

A three tier memory has an upper sub block, a lower sub block, and a middle sub block. In the present disclosure, rather than precharging the upper and lower sub blocks, use is made of the middle sub block using a firmware (FW) scheme. Upon receiving a write request from a host, the FW will route the data to the middle sub block (SB) through reverse order programming (ROP) so that the SBis pre-charged through the source side through the lower sub block (SB). Once the SBis written, data is then routed to the SBand then to the upper sub block (SB). When there is a garbage collection (GC) request, the FW will move the data from the SBand then erase the SB. Then the data moves from the SBand SBis erased. Finally, the data moves from the SBand then SBis erased.

Firmware scheme for 3 tier memories

Some data storage devices select blocks of memory from a free block pool and randomly allocate the blocks as primary and secondary blocks to redundantly store data in a write operation. However, some blocks, such as blocks on the edge of a plane, may not serve well as primary blocks. One example data storage device presented herein addresses this problem by allocating such blocks as secondary blocks instead of primary blocks.

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Kochi, India

Manoj M Shenoy