Western Digital&s PCIe 3.0 x4 WD Blue SN550, which was released at the end of 2019, is still currently one of the fastest inexpensive NVMe SSDs. It achieves a sequential read speed of 2,400 MB/s and a write speed of 1,950 MB/s - at a price of around 76 Euros (1 TB).
However, the case now seems to occur, which is why advisors always point out to check the current technical data of the models in question when selecting SSDs: According to a Chinese tech site, Western Digital is said to have replaced the NAND flash in new versions, which results in a strongly reduced performance in some use cases. Thus, after the 12 GB SLC cache of the WD Blue SN550 is full (which happens especially when writing large files), the write speed of the new version is said to be only 390 MB/s instead of the 610 MB/s of the original version. The reason for the hardware change is probably the current chip shortage.
WD Blue SN550 M.2 SSD
Normally, the memory of current SSDs consists of a lot of slow NAND flash memory as well as a smaller buffer of faster flash memory - only when the latter is addressed, the maximum write speed is reached. The size of this fast buffer varies between a few gigabytes and dozens of gigabytes depending on the SSD model. As long as the data to be written does not exceed the size of the cache memory when working with an SSD, the user will not notice a slowdown in the write rate. However, when working with RAW/4K/6K/8K video, huge files are often copied that exceed the size of the fast cache by far - so a slowdown of the write rate quickly has a noticeable effect here.
This change is problematic at WD mainly because the performance is clearly worsened, but not made transparent for the users, who have to assume that the same technology is used throughout, regardless of the age, when a model is named consistently. Changes of hardware components - often to the detriment of performance - are also known from large SSD manufacturers like Kingston, Adata, Patriot and Crucial.
Samsung has also changed components in its SSD 970 Evo Plus model, but in this case the performance is higher than before in some cases because the write speed of the fast SLC cache has been increased from 1.8 GB/s to 2.6 GB/s and the size from 40 to 115 GB - but there is a drop in write speed to half when the cache is full. Samsung has also clearly communicated the change with a new packaging.
Fortunately, Western Digital has reacted quickly to the developing story and on the one hand confirmed that the NAND flash of the WD Blue SN550 has been replaced and the updated from June 2021, but the changes are also supposed to be found in the data sheet of the new version. In addition, Western Digital is committed to introducing a new model number in the future when changes are made to an existing internal SSD if the associated published specifications are affected.