When using a Raspberry Pi, the performance of your SD card can greatly impact your overall experience. In the past, we have got few Pi sd cards and tested them to test and recommend third-party SD cards if they are any good for your singleboard PCs. However, with the development of more advanced cards, particularly Class A2 models, this process has become more complicated.
To ensure the best possible performance at an affordable price, Raspberry Pi has teamed up with Longsys to create official Raspberry Pi SD cards. These Class A2 cards are designed to offer excellent random read and write speeds across all Raspberry Pi models. For Raspberry Pi 5, they also support command queueing, which further enhances performance.
From now on, Raspberry Pi SD cards will be promoted exclusively by our Approved Resellers, so you can trust their quality for all your Raspberry Pi projects.
Why Choose Class A2 SD Cards?
Class A2 SD cards, like the new Raspberry Pi branded cards, are engineered for faster read and write operations. Raspberry Pi 5 is equipped with hardware that maximizes the benefits of these features. To unlock the full potential of these cards, you need to use the latest version of Raspberry Pi OS. You can update your system with the following command:
sudo apt update && sudo apt full-upgrade
The key to the enhanced performance of Class A2 cards lies in a technology called Command Queueing Host Controller Interface (CQHCI). Let us dive deeper into how this technology works.
What Is CQHCI?
The SD Host Controller Interface (SDHCI) standard defines how an SD card communicates with the system. On Raspberry Pi, the host controller is integrated into the Broadcom application processor. CQHCI builds on top of SDHCI by adding extra control registers and a command queue engine, which takes over when the Raspberry Pi detects a compatible SD card.
In CQ mode, new commands allow the system to manage multiple read and write operations more efficiently, especially for random I/O tasks, which are common in Raspberry Pi OS. This means the SD card can handle multiple operations simultaneously, increasing overall performance.
How Do SD Cards Perform in CQ Mode?
Not all SD cards are equally compatible with CQ mode. While some cards, like SanDisk’s Extreme series, work reliably, others may struggle with certain features, preventing full use of CQ mode. In some cases, the cards may fail to activate CQ mode entirely, leading to performance issues. If you encounter any problems with Class A2 SD cards, you are encouraged to report them on the Raspberry Pi forums.
One risk with enabling CQ mode is that it introduces new possibilities for data corruption if power is lost unexpectedly. Since CQ mode allows the SD card to manage multiple write operations, sudden power loss can result in incomplete writes. To prevent this, Raspberry Pi limits the number of pending writes in CQ mode, which helps to reduce the risk of file system corruption. The result is a high-performance SD card that delivers optimal speed on Raspberry Pi 5 and still provides noticeable improvements on older Raspberry Pi models.
How to Use CQHCI
To make use of CQ mode, your SD card needs to support several specific features, such as performance enhancement registers and power management options. Raspberry Pi OS already supports CQ mode for eMMC cards, and the process for enabling it on SD cards follows similar principles. With CQHCI enabled, data commands are processed more efficiently, allowing for smoother performance during intensive tasks.
As of early 2024, CQ support for SD cards has been fully integrated into Raspberry Pi OS, allowing users to take advantage of this performance boost. By understanding how Raspberry Pi SD cards and CQHCI technology work, you can make better-informed decisions for your Raspberry Pi projects, particularly when performance is a priority.