There are some good reasons why sustained speeds cannot be stated, heat being just one of them. Depending on how well heat is dissipated, thee speed of a card will vary for one.
Note the reccomendation to swap out cards due to the heat, not the capacity.
Speeds of this magnitude have never before been available in storage media specifically designed for the photo and video market, but unfortunately there is a small trade-off. PCIe-based products tend to generate a large amount of heat, which in excess can be harmful to the media, camera, and even the user. This explains why computers utilize fans and cooling systems to regulate the machine’s internal temperature. In order to ensure protection for all involved, the controller used employs an on-die thermal sensor and multiple throttling states to keep its temperature below 90°C (194°F) during usage. When the controller temperature exceeds 88°C (190.4°F), the controller starts the thermal throttling process and 1st throttling state (“Light Delay”) is triggered during which performance speed is reduced by 30%. If the temperature hits 90°C, the controller will go into the 2nd throttling state (“Heavy Delay + Frequency Reduction”), reducing original performance speed by 50%. Thermal throttling states will be triggered as long as the controller’s temperature range is within 86 – 90°C. Once it reaches 86°C (186.8°F), the card (or drive) will either return to the previous throttling state or leave the thermal control mechanism and re-apply the full speed performance.
Now, you may be wondering how long it will take for your card (or drive) to reach that temperature range, but unfortunately there isn’t a straightforward answer. Various factors can contribute to how quickly that may happen, including outside ambient temperature, host, mode, and operation time. For example, a CFexpress memory card used in a Canon 1DX Mark III that is continuously recording 5.5K 60fps 12-bit RAW video at 2600 Mb/s will most likely last longer in a cooler environment than somewhere hotter. In comparison to CFexpress cards, external SSDs (e.g. Delkin USB 3.2 JUGGLER™) will experience the heat issues differently as they are used outside of the camera, but also due to how each is designed and what materials and components are used.
To make sure everything you intended to capture is safely stored without corruption or dropped frames, we recommend having at least one additional card (or drive) on-hand. Check the heat of the storage from time-to-time by using your hand, and if it is too hot to handle, swap it out with a “fresh” unused unit so that the one that was just used can cool down – ideally someplace cool and dry. Going back-and-forth between cards (or drives) to give each “rest” will ensure peak performance and increase longevity.
Performing a full-format on your product regularly is also recommended as it will completely remove any data lingering from a previous recording, which can possibly cause issues in the middle of shooting. Despite if a quick format was done, data from old files remain and that buildup can slow down the sustained write speed of the card (or drive), forcing the camera to stop its current activity. This tends to occur more when recording continuously in demanding video modes, such as 4K at high frame rates and bitrates. To guarantee maximum video recording performance, full format regularly and after extensive use.
Specific only to PCIe-based external solid-state drives, it is important to use either the USB cable that came with the product or only high-speed rated cables. Not all USB cables are built and designed the same, so even though a cable off eBay may cost less, it may limit advertised speeds and what your camera can do. The cables included with Delkin’s JUGGLER™ USB 3.2 SSD (USB Type C-to-C and USB Type C-to-A) have been tested extensively in order to guarantee speeds as advertised.
Despite the slight heating issue, the benefits PCIe-based products provide far outweigh the side effects. The technology offers the fastest available speeds on the market, opening up new, exciting possibilities for photographers and videographers of any skill range.