Comment by supertrope

The DRAM cache does not hold user data. It holds the flash transition layer that links LBAs to NAND pages. Higher performance drives use 1GB of DRAM per 1TB of NAND. In cheap DRAM-less drives if the I/O to be serviced is not cached in the 1MB or so of SRAM it has to do a double lookup. Once to retrieve the full FTL table from NAND and a second lookup to actually service the I/O.