pSLC Cache / Write Intensive Usage

When copying games from your Steam Library, or other very large files (>10 GB), you may notice that write speeds on your SSD start at full speed, before dropping considerably. The underlying reason is that modern drives have small, fast 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 pseudo-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, something most consumers will never do.


Write speed starts out at almost 5 GB/s, with some up-and-downs in-between. This rate is sustained until 207 GB have been written to the drive. Once the SLC cache is full, write speeds drop to around 2.5 GB/s, which is still excellent. Once the drive is almost completely full, speeds drop further, to around 750 MB/s.

Filling the whole 2 TB capacity completed at 1.8 GB/s, which is a very good result, in-line with the major competing drives.