The Canon 70D DSLR camera supports a minimum SD (UHS-I) card speed of 20 Megabytes/sec to utilize burst mode shooting and record full 1080HD videos. When choosing SD cards, it’s often difficult to determine what speed will meet the minimum requirements as the cards often tout the maximum read speed under ideal conditions. The more important number is the write speed since that is what will limit the performance of the camera. Some play it safe and recommend 90 MB/s cards but those are expensive and overkill unless the objective is to speed up transfer of image/video from the card to the computer.
This test compares the read/write performance of the SanDisk Extreme 32 GB SDHC Class 10 UHS-1 Flash Memory Card 45MB/s SDSDX-032G-AFFP against the Sony 64GB SDXC Class 10 UHS-1 R40 Memory Card (SF64UY/TQMN) transferring data between card and computer. The tests were done using a Transcend Information USB 3.0 Card Reader (TS-RDF5K) to remove any bottlenecks from a USB2 channel.
Test conditions and disclaimers
- Transfer speeds from a card to the computer is not indicative of performance in camera.
- Transferring one large file like a video file is faster than transferring the same amount of data comprised of many small file such as jpg file. (The test uses a 500 mb file)
- Many factors such as USB channel, card reader, and HD speed contribute to transfer speeds. This test uses an Intel i5-4670K Haswell cpu in an Asus H87M-Pro Motherboard.
- Testing transfer speed by copying files in Windows is not accurate since it is influenced by Windows cache and HD performance. This test uses HD Tune which transfers random data from memory.
The Sandisk is rated for up to 45 MB/s. As indicated in this screencap, it performs at 46 MB/s read and 38 MB/s write.
The Sony is rated at up to 40 MB/s. Actual speed is 46 MB/s read and 20 MB/s write barely meets the 70D’s minimum requirement.
USB 2 performance in computer
But what if you have an older computer or laptop limited to USB 2. Here is what you can expect for card to computer transfers. Of course, in camera performance is not affected.
Sandisk – 28.7 MB/s read, 24.7 MB/s write.
Sony – 28.8 MB/s read, 19 MB/s write.
Although the tests were done using the Sandisk 32 GB card, the 64 GB card in the same family should have the same performance. The SanDisk Extreme 64 GB SDXC Class 10 UHS-1 Flash Memory Card 45MB/s SDSDX-064G-X46 is just under twice as much as the Sony card. If you want faster transfer times to the computer, choose the faster Sandisk card.
But wait! What about in camera performance?
Test #1: High speed shooting test shooting RAW. Sandisk recorded 20 frames before filler the buffer slowing down. Sony recorded 17 frames before slowing down. Presumably, the Sandisk is able to flush the buffer faster allowing more frames to be recorded. If high speed shooting is important to you, the Sandisk outperforms the Sony card once again. The Sony card is not slow by any means and will work just fine for most shooters.
Test #2: Slow cards will cause the camera to stop recording video. In tests performed on both cards at 1080 @ 30fps and 720 @ 60 fps, both cards recorded w/o incident.