A Look Inside Micron's M500DC
Though the M500DC shares its architecture with the M500, opening up the new SSD's chassis shows that they're actually quite different. The first thing you'll notice is how empty the PCB appears. There's so much room, in fact, that Micron left what we assume are debug headers across one side of the board.
Micron has so much available space because the M500DC employs high-density NAND. The 800 GB model has 1024 GB of 20 nm MLC flash spread across eight packages. It's not of the eMLC variety. But still, Micron bins it specifically for more enterprise-oriented products.
The M500DC and M500 have the same type of NAND in common. However, when you open up an M500, you'll see all eight packages on one side of the PCB. The M500DC sports four per side. Each package contains eight dies, totally 1 Tb (128 GB) of capacity. Freeing up extra room allows Micron to also ship the M500DC in a 1.8" form-factor, in addition to the 2.5" drive we're reviewing. We didn't have a chance to benchmark the 1.8" model, however, you can see how the components would fit in a 1.8" footprint.
If you looked closely at the specifications on the previous page, two data points probably jumped out at you. First, the 800 GB M500DC has identical write endurance and lower random write performance compared to the 480 GB model. How is that possible? The more NAND your drive includes, the more flash there is to spread write amplification across and the higher endurance should be. It's just that simple.
When we opened the 800 GB model, we encountered the expected 1024 GB of NAND. So, what's going on with the other capacities to explain the difference? It turns out the the smaller drives include nearly double the amount of over-provisioning compared to Micron's 800 GB version. The 480 GB M500DC comes equipped with six packages, for instance, instead of the four you'd expect, yielding a raw total of 768 GB. As we know, the more NAND the controller has to work with, the more efficiently it can apply its software algorithms.
Micron uses the same venerable Marvell 9187 that appeared on its M500, and heat is removed from it through thermal pads attached to the chassis. Of course, Micron applies its suite of enterprise-oriented firmware features (XPERT), which takes NAND management to a level appropriate for that market. I discussed the features at length in Micron P400m SSD Review: High Endurance MLC Is Here To Stay, but here are the highlights:
- Redundant array of independent NAND (RAIN): An architecture that essentially provides device-integrated algorithms that are RAID 5 across the flash channels.
- Advanced Read Mangement/Optimized Read (ARM/OR): This feature uses DSP algorithms to optimize NAND read and write locations.
- DataSAFE: A data path protection mechanism that ensures all information is transferred correctly through the SSD structures.
- Physical Power-Loss Protection: This feature uses on-board capacitors to continually store power for emergency use.
- Reduced Command Access Latency (ReCAL): Utilizes well-managed background operations for quicker response times.
Additionally, the M500DC sports two 512 MB DDR3 DRAM packages, one on each side, yielding a fairly standard 1 MB per gigabyte DRAM to NAND ratio.
Finally, the top of board is populated with 12 capacitors used for power-loss protection.
