DirectStorage shows only minor download speed improvements in a real PC demo

The Microsoft DirectStorage API promises to speed up game downloads on both Xbox Series X/S and Windows PCs (where Microsoft recently exited the developer preview phase). One of the first games to showcase the benefits of DirectStorage on PC is Square Enix’s Forspoken, which Luminous Productions CTO Teppei Ohno showed off at GDC this week. As reported by The Verge, Ono said that thanks to the fast NVMe SSD and DirectStorage support, some scenes in Forspoken can load in as little as one second. This is definitely an improvement over CD and DVD loading times of yesteryear.

However, as a DirectStorage demo, the Forspoken numbers are a mixed bag. On the one hand, the examples Ohno showed clearly show faster loading of DirectStorage scenes on the same hardware compared to the legacy Win32 API – from 2.6 to 2.2 seconds in a single scene and from 2.4 to 1.9 seconds in another. Forgotten showed performance improvement on older SATA-based SSDs as well, despite being positioned as a feature that would primarily be useful for NVMe drives – a drop from 5.0 to 4.6 seconds in one scene and from 4. 1 to 3.4 seconds into another. Speed ​​improvements for SATA SSDs have been limited for the better part of a decade because the SATA interface itself (not the SSD controller or NAND flash chips) is holding them back.

On the other hand, Ono’s demo showed that the game’s load times didn’t improve as dramatically as the raw I/O speed would suggest. On the NVMe SSD, I/O increased from 2862 MB/s using Win32 to 4829 MB/s using DirectStorage—an increase of nearly 70 percent. But the loading time of the scene has decreased from 2.1 to 1.9 seconds. This decline would not be noticeable even if you tried to notice it.

The Forspoken demo ended up showing that the speed of the storage you use is still much more about how fast your games load than DirectStorage does. One scene that took 24.6 seconds to load using DirectStorage on HDD loaded in just 4.6 seconds on a SATA SSD and 2.2 seconds on an NVMe SSD. This is a much larger gap than between Win32 and DirectStorage running on the same hardware.

Please note that this is just one game and we will likely see a wider range of results as more developers implement DirectStorage into their games and as Microsoft refines the technology. Eliminating other CPU bottlenecks, including moving resource decompression from the CPU to the GPU, can further increase the performance advantage of DirectStorage. GPU decompression is not yet supported in the PC version of DirectStorage, but Microsoft claims the feature is “next on our roadmap”.

Listing image from Western Digital