When I recently bought my new Lenovo X13 notebook with an AMD Ryzen 7 4750U CPU with 8 cores / 16 threads, I had to make a small compromise: I had to buy a rather low end 2 TB NVMe SSD to replace the small SSD it came with, as more expensive but better SSDs would not have reached me in time. It turned out pretty quickly however, that this SSD had a significant downside: The amount of data that can be written to it at full speed is quite limited and any write operations afterward are very slow.
Like most consumer NVMEs, the 2 TB Crucial P2 I bought has a certain amount of fast flash memory to which data can be written at a very high speed. But once that part is full, further writes go to the much slower flash memory. Once there is no more data written to the drive for some time, data is copied from the fast flash memory to the slower part of the drive to make room again for fast bulk data transfers.
For small data transfers this is not an issue. For example, when I copy a couple of GBs of data from a RAM disk to the drive, the data rate exceeds 1 GB/s. That’s a very nice value and a big improvement over SATA speeds! Unfortunately, I do have two real world scenarios in which I copy huge amounts of data to the internal SSD, and here, the P2 does not perform well at all:
Every now and then I want to copy virtual machine images from a workstation over a 2.5 GbE link to the notebook. And these are really huge, 100+ GB is not an exception. My notebook can get around 200 MB/s out of the 2.5 GbE link, so that’s the minimum sustained speed I require the SSD to support. What can be observed, however, is, that after around 80 GB, SSD write speeds suddenly drop to a constant 100 MB/s. In real life, that means a significant delay to the overall process that can be measured in minutes.
And my second scenario in which this behavior is a real deal breaker: Migrating an existing system to a new NVMe. Here, the amount of data is usually > 1 TB, so a sustainable write throughput of 100 MB/s is totally unacceptable as well, and the delay can be measured in hours. Even a hard disk can do better…
As a result, I bought a 2 TB Samsung 970 Evo Plus which should do much better for my two use cases. Stay tuned for the follow up post with the results.