The presence of factory bad blocks in NAND flash is as much a technology reason as the occurrence of additional bad blocks during the lifetime.
Both are no (negative) quality indications. However, with the occurrence of bad blocks during the lifetime, the correct handling of these events by the firmware is critical in
order not to lose the new data as well as the already stored data of such blocks.
To compare speed specifications in data sheets of NAND flash memory media, the test conditions must be identical. If the measurement was not started repeatedly or did not cover the entire logical address space, the specified speed can be significantly higher than the real achievable speed.
Unlike hard drives or NOR flash, NAND flash does not have a fixed mapping of logical
memory addresses to physical memory addresses.
The assignment takes place via mapping tables, which are managed by the firmware of the storage medium.
ENDURANCE - WAF
When it comes to the endurance of NAND Flash products, the Write Amplification Factor plays an important role in maximizing a products usable life.