UPDATE: 5/3/2013 if you’re using mRAW or sRAW in your workflow, check out my recent article to see if you’re actually saving yourself hard drive space.
UPDATED 4/3/2012 to add metric for mRAW to CF, sRAW to SD.
I am in love with my new Canon 5d3. A huge sigh of relief for me is the dual card slots, so I can always have a backup. Unfortunately there’s a big performance difference between the SD card slot and the CF card slot.
If Canon had chosen to support the UHS-1 standard, we’d get roughly equal performance. As it is, they supported SDXC, but not UHS-1. (For the record, the camera will work with a UHS-1 card, it just won’t support the improved write speeds. I’m using one in my camera and it works fine.)
Assuming you’re not using super old CF cards, the write speed of the SD card represents the bottleneck, and is what will limit how fast the camera flushes the data from the buffer. Given this, I suspected that writing RAW to the CF card, and mRAW to the SD card might help speed things along. The SD card data is only there for an “oh shit” moment, and under these conditions mRaw’s 10-ish megapixels ought to be good enough to get by.
There’s a gotcha, however. When writing the same file to one or both cards, the buffer gives us a solid 12 frames before hitting the bottleneck. When writing different files though, we lose roughly half the buffer.
For example, configuring the camera to record full RAW to the CF card, and either mRAW or sRAW to the SD card results in a 6 frame buffer. Configuring the camera to record full RAW to the CF card, and JPEG (regardless of size/quality) to the SD card results in a 7 frame buffer. It stands to reason that a chunk of the buffer memory is being utilized to generate two different versions of the file.
So the question is, would you rather have a bigger buffer and slower flush speed, or a smaller buffer and faster flush speed? Only you can answer that question for yourself, but here are some speed comparisons to help you decide.
This trial is not intended to test performance of any particular memory card. It is intended to compare different write settings within the camera on a given set of memory cards.
To test, I used one 64GB 400x Lexar Professional memory card, and one 64GB LX Series Patriot Memory SDXC card (class 10 / UHS-1). For each test I held down the shutter button until the buffer filled, then waited for the shutter to click ten more times. You can see the difference simply by looking at the recording. The longest tracks took the longest to complete.
In order of performance, times approximate, measured to highest peak on the last recorded shutter click:
- 6.9s, Full RAW to CF card only (super fast – no surprise)
- 9.8s, mRAW to CF card, sRAW to SD card. (Interesting how it takes a long time to warm up, then runs pretty quick.)
- 13.8s, Full RAW to CF card, Large/Fine JPEG to SD card.
- 14.4s, Full RAW to CF card, mRAW to SD card.
- 18.1s, Full RAW to SD card only
- 18.6s, Full RAW to both CF and SD cards
Again, remember that options 2 through 4 in green, while completing the test faster, also limit you to a 6 or 7 frame buffer.
Your workflow will determine which option is best for you.
Which will you use and why? Tell us in the comments below!