TS-4100 MicroSD Card Interface
The i.MX6UL SDHCI driver supports microSD (0-2 GB), microSDHC (2-32 GB), and microSDXC(32-2048 GB). The cards available on our website on average support up to 16MB/s read, and 22MB/s write using this interface. Sandisk Extreme cards with UHS support have shown 58MB/s Read and 59MB/s write. The Linux driver provides access to this socket at /dev/mmcblk0 as a standard Linux block device.
See the i.MX6UL reference manual for more information on this controller.
We have performed compatibility testing on the Sandisk microSD cards we provide, and we do not suggest switching brands/models without performing qualification testing. Though SD cards in theory will all follow the standard and just work, in practice cards vary significantly and can fail in subtle ways. We do not recommend ATP or Transcend microSD cards specifically due to known corruption issues that can occur after many GB of written data.
Our testing has shown that on average microSD cards will last between 6-12 TB of written data before showing a single bit of corruption. This is enough for most applications to write for years and not see any issues, but for more reliable consider the eMMC which is expected to last over 100 TB of writes. Higher end SD cards can also extend this, but industrial grade SD cards typically carry a cost much higher than the eMMC.
SD cards in general should not be powered down during a write/erase cycle, doing so will eventually lead to disk corruption. It is not always possible for 'fsck' to recover from the types of failures that will be seen with SD power loss. The system should be designed to avoid power loss to SD cards, or the eMMC module should be used for storage instead which can be configured to be resilient to power loss.