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 close to 1.2 GB/s and stay high until 356 GB (a lot!) have been written, which is roughly one third of the whole drive. This is strong evidence that the Realtek controller will use the whole TLC capacity of the drive in SLC mode, which is excellent for soaking up large write bursts. Once the cache is exhausted and the drive is full, the controller has to copy existing data from SLC into TLC to free up space to reach its advertised capacity, all while handling the incoming stream of data. At this point write speeds are very poor, reaching only 200 MB/s on average, but sometimes dipping down to below 100 MB/s.

With an average write speed of 308 MB/s, the Falcon does considerably better than similar-priced QLC drives in our test group. Against high-end M.2 NVMe drives it falls behind, though. Once write activity stops and the drive is idle, pSLC cache gets flushed to TLC in the background and full write performance is restored.