BCH codes for solid-state-drives

Abstract

Given that the NAND Flash memory is not a very reliable medium, it follows that a Solid State Disk needs some help to achieve a reliability suitable for computing applications: the Error Correction Code (ECC). As the NAND technology scales down, ECC becomes a critical design topic. This chapter deals with BCH, the most common ECC in solid state disks. Two main issues arise when an ECC is used inside an SSD. First of all, the ECC should not limit the bandwidth, being the bottleneck of the entire drive: this translates in a hardware implementation that needs to handle multiple devices (channel) in parallel. At the same time, ECC must avoid erroneous corrections when the error correction capability of the code is overcome, i.e. it must have a high detection property. In this chapter the ECC definitions are reviewed, then the BCH code is presented along with the multi-channel topic. Finally, BCH and LDPC detection property are discussed.