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Crucial's m4: Not Old, Not New
Similar to the SSD 320-series, Crucial's newest drive is more of a refresh than a completely new product. These two product launches are really driven by the shift over to 25 nm NAND flash.
Beyond the rebranded name and memory, there isn't much difference between m4 and its predecessor (Crucial's RealSSD C300 review). The improved specs are primarily the result of the new 25 nm process. Sequential read performance sees a small bump up to 415 MB/s, while sequential write performance is now 260 MB/s. In comparison, random read performance has dropped to 40 000 IOPS, but random writes have increased to 50 000 IOPS.
|Crucial RealSSD C300 128 GB||Crucial RealSSD C300 256 GB||Crucial m4 128 GB||Crucial m4 256 GB|
|Sequential Read ||Up to 355 MB/s||Up to 355 MB/s||Up to 415 MB/s||Up to 415 MB/s|
|Sequential Write ||Up to 140 MB/s||Up to 215 MB/s||Up to 175 MB/s||Up to 260 MB/s|
|4 KB Random Read||Up to 50 000 IOPS||Up to 60 000 IOPS||Up to 40 000 IOPS||Up to 40 000 IOPS|
|4 KB Random Write||Up to 30 000 IOPS||Up to 45 000 IOPS||Up to 35 000 IOPS||Up to 50 000 IOPS|
|Cache||256 MB||256 MB||256 MB||256 MB|
|NAND Flash Components||34 nm MLC, ONFI 2.1||34 nm MLC, ONFI 2.1||25 nm MLC, ONFI 2.2||25 nm MLC, ONFI 2.2|
|Raw NAND||128 GB||256 GB||128 GB||256 GB|
|Interface||SATA 6Gb/s||SATA 6Gb/s||SATA 6Gb/s||SATA 6Gb/s|
Inside Crucial's m4
Micron tells us this is the same Marvell 8SS9174 controller seen in Crucial’s C300, with a slight revision for ONFI 2.2 compatibility. Architecturally, nothing has changed. Even though the labels suggest three different generations, this is more a matter of firmware.
At the controller's core, there are two ARM9 processors which operate in tandem; one handles host request and other handles NAND requests. Some load balancing occurs when demand on one processor gets too high.
Micron has carried the massive 256 MB cache employed on the C300 over to the m4. Only the 64 GB models have 128 MB. The cache is used mostly for temporary functions, such as table mapping and write tracking. Whenever a write occurs, the controller performs a bit of cleanup to ensure there are enough clean blocks to prevent any performance slow-down, and when the drive sits idle, some garbage collection occurs. This functions independently of the OS, and it's a recipe that Micron believes best preserves performance.
We are still waiting on pricing information for the m4. We are told that the new drives won't be as expensive as the C300's launch prices, but that's fairly vague. The C300 hit the scene with a suggested price of $149.99 (64 GB model), $299.99 (128 GB model), and $599.99 (256 GB model). At close to $2.50 per gigabyte, it was a fair deal, but nothing we would get excited over. Today, the C300 hits close to $2 per gigabyte, and we are hoping the m4 introduces further drops to the C300's price.