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 an impressive 2 GB/s. The drive sustains these write rates until around 150 GB have been written. At this point, the SLC cache is full, and the drive will start flushing SLC back to TLC, which has an effect on write rates. With 500 MB/s in that state, speeds are still reasonably high—matching the best SATA drives. Once over 600 GB have been written without pause, rates drop a little bit further, to 400 MB/s. The average of 480 MB/s is better than most other value-oriented TLC drives on the market. Once the SLC cache has been flushed completely, write rates jump back up to full speed—this process repeats for the whole duration of our test.