WD AN1500
SSD Specification and Info
WD AN1500 is an High-End NVMe SSD produced and sold by WD. The device comes with x8 PCIe 3.0/NVMe interface and AIC form factor - a good fit for both desktop and laptop computers. This SSD has a maximum sequential read-write speed of up to 6500/4100 MB per second, making it ideal for gaming and workstation PCs.
WD AN1500 is equiped with DRAM memory, and a TLC NAND flash memory with 96 cell layers.
NAND type
WD AN1500 is using a TLC (3 bits per cell) NAND manufacurted by SanDisk with 96 cell layers on top of each other.
The TLC is the most common type of SSD NAND flash memory found on the market at the moment. It is faster, less durable, but still cheaper than the other, more expensive variants - SLC and MLC.
The main advantage of this type of NAND chips is the fact that the cost per gigabyte is much lower, allowing high capacity SSDs at affordable price.
The Controller
WD AN1500 is using 2xWD + 88NR2241 SSD controller to connect the NAND memory to the x8 PCIe 3.0/NVMe interface. The controller has 2xSN750 controller + RAID configuration.
Typically, SSD controllers are microprocessors. In this case we have 2xSN750 controller + RAID processor responsible for controlling the SSD in such way, so that the data coming from the interface can be stored on to the NAND flash memory.
Some SSDs have simpler controllers with fewer communication channels and less cores.
Among other things, the controller also manages the SLC caching, optimizing the DRAM cache, encryption, LDPC, garbage collection, wear-leveling as well as TRIM
DRAM Cache
WD AN1500 has a separate DRAM chip to store the SD mapping tables. DRAM cache speeds up the data access significantly compared to the DRAM-less models.
As soon as the OS requests some data from the SSD, the SSD needs to know exactly where it is on the drive. Because garbage collection moves the data constantly, the controller relies on the mapping tables to locate it.
These tables are stored in DRAM cache, where they are accessed much more quickly than in NAND flash.
Therefore, SSDs with DRAM-less architecture have more random write and read operations. This makes the device perform worse and last shorter if they are not HMB enabled.
HMB Support
There is no HMB architecture available on the WD AN1500 to store the mapping tables. The device either doesn't support the architecture or uses DRAM cache.
The HBM is used to reduce the cost of production of NVMe SSDs with DRAM Cache, SSDs with this type of controllers can leverages the host system's DRAM instead of an onboard DRAM chip to host the FTL mapping table used by flash storage.