New WD SN550 SSDs allegedly crippled to half write speeds when out of SLC cache

The Blue SN550 from Western Digital (WD) is one of the most popular budget NVMe SSDs available in the market.

However, according to a report by Chinese media outlet Expreview, the company is allegedly crippling the write performance of the drive, at least on the 1TB model, once the available single-level cell (SLC) cache is exhausted on the newer batches of the product that are available for purchase nowadays.

The SN550 comes with 12GB of SLC cache and after that amount is exhausted, the write speeds on the newer variant apparently drops down to around 390MB/s in the TxBENCH storage test, whereas the original model could do 610MB/s in a 100GB copy test (via Tom's Hardware).

While Expreview hasn't provided any numbers for the original SN550 in the TxBENCH write test, it has noted that the speed is actually even lower than half in the new version and according to it, the speed is seemingly comparable to the WD Green SN350 model. It has been stated however that the speeds remain unchanged as long as the SLC cache isn't saturated.

The SN550 is a DRAM-less drive that utilizes Host Memory Buffer (HMB) technology and SLC caching to compensate for that. The HMB allows the SN550 to borrow some part of the system DRAM when needed while the SLC caching acts as a performance booster where a part of the TLC NAND (in this case, 12GB) emulates SLC for faster burst performance.

Expreview has noticed that the new SN550 variant comes with a newer flash memory version and firmware.