Write Intensive Usage

When copying games from your Steam Library or other very large files (>10 GB), you might have noticed that write speeds on your SSD start out at full speed and then drop considerably. The underlying reason is that modern drives have caches that soak up write bursts to improve performance. In the fairly uncommon scenario of writing data that's too big to fit into these caches, the drive will have to write data directly to flash, and it will probably juggle some out of its write cache at the same time, which can result in a significant loss of write speed. Newer TLC drives use part of their capacity in SLC mode for increased performance. This test can reveal the size of that SLC cache.

Testing on this page looks at exactly that scenario. We write a sequential stream of 1 MB blocks to the drive in a single thread, like a typical file-copy operation would do, and measure write speeds twice a second. The drive is fully erased before testing to ensure any caches are emptied. Please note that this test writes a lot of data in a very short time, which is something most consumers will never do.


Write speeds start out at almost 3 GB/s and remain high until 208 GB of data have been written. This SLC cache size is good, and should be able to handle all but the large bursts of write activity. Once the SLC cache is full, the controller is writing to TLC directly, which runs at around 800 MB/s. Once half the drive's capacity is used up, speeds drop to around 300 MB/s.

Filling the whole drive completes at 431 MB/s, which is a fairly low result, slower than many competing value-NVMe drives out there. Given the positioning, it is highly unlikely you'll be writing that much data in such a short time, though, so you'll probably never even hit the limits of the SLC cache.

Any pause in write activity, even for a second, will give the drive time to free up some SLC cache, so full write rates are restored after some idle time even if the drive is partially filled.