Bogdan Stăncescu

Things to consider when shopping for an M.2 drive

Things I learned today about M.2 drives:

• Disclaimer: all of this is a gross simplification and a terrible abuse of notation, but this post is intended for the casual geek shopper; I worry little for the experts;
• M.2 ⊂ SSD ⊂ NAND ⊂ flash memory ⊂ EEPROM ⊂ NVRAM ⊂ computer memory
  • All EEPROM is organized into conventional memory cells with variable storage capacity per cell;
  • All EEPROM cells are susceptible to failure after a given number of write cycles;
    • Irrelevant factoid: NAND is not not an acronym–it stands for Not And memory (as opposed to the other kind of Flash memory). I say it’s not not an acronym because people tend to assume acronyms are restricted to initial letters of words, when acronyms are in fact absolute beasts which can devour entire groups of letters at the beginning of words!
• You definitely want PCI Express, not SATA III;
  • Even low end PCI-E M.2 drives are roughly 4x faster than SATA III drives of any kind;
• You probably want MLC, not any of the other ones
  • *LC (*–Level Cell) indicates how many bits are written per memory cell. Given the production costs per cell, the write rate limitations per cell, and the MTBF per cell, packing more bytes per cell reduces costs, but it also limits overall data throughput and the drive’s lifespan;
  • MLC is in the serious hobbyist’s Goldilocks zone for the level cell size:
    • SLC (1x) is the best of the best, but it comes at a serious premium; MLC (2x) is below premium but above consumer level, then TLC (3x), QLC (4x), and at some point in the future PLC (5x);
• You might want 3D technology, if you’re willing to spend extra;
  • 3D memory storage sounds like marketing mumbo-jumbo, but it’s a serious technological leap. You can only pack so many cells on a 2D rectangle before you reach interference limits caused by fundamental physics – and the M.2 form factor does impose physical size limits. Although height is just as limited as length or width, it’s way more efficient to double the very tiny height of the board than it is to halve its very large length and still keep the cells isolated from interference and ultimate failure.