The good people over at the Raspberry Pi Foundation questioned whether class is the only meaningful metric. Based on their tests, there are variations in brands and other qualities/attributes of SD cards which can have a meaningful impact on Raspberry Pi IO performance. Therefore, I decided to buy a different class 10 card (albeit a better class 10 card) to see how it’s performance might be different from the class 10 card I tested.
I will admit up front, the SanDisk card is a nicer card based on specs alone. Unlike the Transcend card, the SanDisk card is a “UHS” or “Ultra High Speed” card designed for high speed transfers. The SanDisk is sold as an extreme SD card. This card is also more expensive at $13 for the 8GB model. With that in mind, I wanted to see if, given a budget of ~$12 (which I spent on the Transcend card) this SanDisk card would be worth it.
To benchmark the IO performance, I used Phoronix Test Suite v4.4.1 with the Dbench 4 test. All services which would cause disk performance degradation were stopped. The two units were set up identically (same file system, services, etc.)
As with the last test, these results show a signifiant difference in performance between the two cards. The Transcend had an average transfer rate of 5.75 MB/sec while the SanDisk card had an average rate of 12.56 MB/sec.
Phoronix Test Suite v4.4.1 System Information Hardware: Processor: ARMv6-compatible rev 7 @ 1.00GHz (1 Core), Motherboard: BCM2708, Memory: 470MB, Disk: 8GB SU08G Software: OS: Debian Linux 7.0, Kernel: 3.6.11+ (armv6l), Compiler: GCC 4.6, File-System: ext4, Screen Resolution: 656x416 Dbench 4.0: pts/dbench-1.0.0 [Client Count: 1] Test 1 of 1 Estimated Trial Run Count: 3 Estimated Time To Completion: 37 Minutes Started Run 1 @ 15:45:47 Started Run 2 @ 15:57:51 Started Run 3 @ 16:09:53 [Std. Dev: 1.44%] Test Results: 12.4025 12.7599 12.5291 Average: 12.56 MB/s
If performance matters, especially for small-scale (very small scale) server applications or other IO-intensive tasks, than getting a smaller but higher-performance SD card may be the best cost-benefit decision.