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  1. #1
    Super Moderator Kayaker72's Avatar
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    Dec 2008
    New Hampshire, USA

    CFExpress Cards Speed Tests

    Let me start off by stating, I do not expect that I will often use top end specs of an R3 or R1 camera. Heck, for the R5, I do use the 20 fps, but I do not fill the buffer, it is for a few second bursts.

    That said, some speculation I have seen really has me wondering about the R1. The speculation is high FPS and high MPs. But, that equates to high data throughput. So, I ran some numbers starting with theoretical max write speeds of CFExpress cards (~1400 MB/sec of actual cards and 2 GB/sec for Type B). But, then I got to thinking no card ever performs as well as rated. So, I played with Bryan's data of # pictures before hitting the buffer on the R5. Based on the numbers, I get the R5 buffer being 4-6 GB, but the write speed of the ProGrade Cobalt card he used only being ~500 MB/sec, or 1/3 of its rated 1500 MB/sec.

    This made me look online, and I did find this article. First, the difference among cards is impressive, even different capacities (Sandisk, looking at you). They published time to clear the buffer on the R5, not MB/sec, but they estimate the buffer to be 2 GB and 4-8 seconds to clear gives the write times to the cards would be 250-500 MB/sec. Way off of the spec. (BTW, they also got very different results to Bryan in terms of pictures to fill buffer, so, something is inconsistent between these tests).

    Their write speeds using a card reader were 450-800 MB/sec. Again, way off the spec, but at least getting closer.

    So, I have always known cards perform at less than their max spec. However, usually they are 50-75% of that spec, not 15 to 33%.

    CFExpress, still better than SD UHS II (which are typically ~180-200 MB/sec), but they are not functioning nearly as well as is being widely assumed.

    I assume with the R1, Canon will want to have something similar to the 1DXIII where it doesn't hit a buffer (rated at >1000 RAW images). But the 1DXIII is only moving ~600 MB/sec with its 20 MB sensor to do that. Canon can not go much higher in MPs before they run into limitations of the actual write speeds to CFExpress cards. Which means one element we may be waiting on a high MP/high frame rate camera is improvements to CFExpress cards. Specifically, looks like current CFexpress Type B cards are PCIe 3.0 x2 lanes and is currently maxed out at 2 GB/sec. Type C (similar in size to old CF cards) with PCIe 3.0 x4 lanes can do up to 4 GB/sec eventually and I saw reference to PCIe 4.0 is eventually coming. But, that also means, if you want the top end specs, we'll likely be looking at new cards.
    Last edited by Kayaker72; 09-28-2021 at 03:53 PM.

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