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 well over 2.5 GB/s, which is very impressive and one of the best results I've ever seen in this test. The drive sustains these write rates until 300 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 1.3 GB/s in that state, speeds are still very high, much better than most other TLC drives on the market. Only when the drive is more than half full do write speeds drop significantly to between 500 and 700 MB/s, which is still better than what the best SATA drives can achieve.

On average, the HP EX950 is one of the fastest SSDs we have ever tested when it comes to this test. Only the ADATA SX8200 Pro does better here, and the MLC-based Samsung 970 Pro, of course. Once write activity stops and the drive is idle, the pSLC cache gets flushed to TLC in the background and full write performance is restored.