Sony has announced a new line of SD cards that aren’t just fast — they’re capable of hitting the fundamental performance limits of the Ultra High Speed II (abbreviated UHS-II) specification. That standard offers up to 312MB/s of performance, while Sony is claiming 300MB read/write speeds for its new line of SF-G SD cards.
The UHS-II standard specifies a 156MB/s data rate when in half-duplex mode (reading and writing simultaneously) and a 312MB/s rate when only reading or writing. Sony’s published claim of 300MB/s reads and 299MB/s writes assumes half-duplex operation, though that’s probably a reasonable assumption since most people aren’t writing 4K video while simultaneously attempting to read it.
These new cards aren’t available in very high capacities, with 32GB, 64GB, and 128GB options available. Other manufacturers have ramped SD cards with 256GB and 512GB capabilities, but Sony is clearly going for performance over capacity with this product family. The 300MB read speed isn’t particularly impressive, but 300MB/s writes is something altogether different.
SD card reviews suggest that a 299MB/s write speed would put the Sony SF-G in a class of its own. HaveCameraWillTravel reviewed a number of SD cards and found only one microSD card capable of maintaining a >200MB/s write speed — the Lexar 1800x. That write performance appears to have come at the expense of read performance, with the 1800x only turning 70.4MB/s of sequential read performance.
According to Sony, its increased performance is the result of firmware tuning and an on-board buffer. Here’s how the company describes it:
With a write speed of up to 299 MB/s, enabled by Sony’s unique firmware, the SF-G Series will be the world’s fastest SD cards… It also contributes to a shorter buffer clearing time so users never miss a critical moment. Using Sony’s algorithm, the cards prevent the decrease of data-writing speeds and contribute to the camera’s ability of successive high speed shooting.
With that said, Sony is glossing over one critically important issue. The performance you’ll get from a camera, 4K or otherwise, isn’t just a function of the speed of the SD card. It’s also a function of the camera’s SD card controller. Imagine plugging a USB 3.0 stick into a USB 1.1 port and you’ll see the problem. A USB 3.0 drive might reach marginally higher performance than its USB 1.1 counterpart, but it won’t come anywhere close to what the interface can actually achieve. According to Tested.com, this is a known problem even on some high-end cameras. While that article dates back to 2013, it captures the issue well. Canon’s 5D Mark III is a $3500 camera with an extremely fast CompactFlash slot and a very slow SD card slot. That camera supports the UDMA7 protocol (167MB/s theoretical transfer rate) for its CF slot, yet failed to support either UHS-I or UHS-II. The SD card was therefore limited to just 25MB/s of maximum performance — vastly slower than its CompactFlash slot.
The new Sony cards should be available for purchase starting this spring.
This article was originally posted on ExtremeTech
By Joel Hruska